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1. Vertex (geometry) – In geometry, a vertex is a point where two or more curves, lines, or edges meet. As a consequence of this definition, the point where two lines meet to form an angle and the corners of polygons and polyhedra are vertices. A vertex is a point of a polygon, polyhedron, or other higher-dimensional polytope. However, in theory, vertices may have fewer than two incident edges, which is usually not allowed for geometric vertices. However, a smooth approximation to a polygon will also have additional vertices. A polygon vertex xi of a simple polygon P is a principal polygon vertex if the diagonal intersects the boundary of P only at x and x, there are two types of principal vertices, ears and mouths. A principal vertex xi of a simple polygon P is called an ear if the diagonal that bridges xi lies entirely in P, according to the two ears theorem, every simple polygon has at least two ears. A principal vertex xi of a simple polygon P is called a mouth if the diagonal lies outside the boundary of P. Any convex polyhedrons surface has Euler characteristic V − E + F =2, where V is the number of vertices, E is the number of edges and this equation is known as Eulers polyhedron formula. Thus the number of vertices is 2 more than the excess of the number of edges over the number of faces, for example, a cube has 12 edges and 6 faces, and hence 8 vertices

2. Edge (geometry) – For edge in graph theory, see Edge In geometry, an edge is a particular type of line segment joining two vertices in a polygon, polyhedron, or higher-dimensional polytope. In a polygon, an edge is a segment on the boundary. In a polyhedron or more generally a polytope, an edge is a segment where two faces meet. A segment joining two vertices while passing through the interior or exterior is not an edge but instead is called a diagonal. In graph theory, an edge is an abstract object connecting two vertices, unlike polygon and polyhedron edges which have a concrete geometric representation as a line segment. However, any polyhedron can be represented by its skeleton or edge-skeleton, conversely, the graphs that are skeletons of three-dimensional polyhedra can be characterized by Steinitzs theorem as being exactly the 3-vertex-connected planar graphs. Any convex polyhedrons surface has Euler characteristic V − E + F =2, where V is the number of vertices, E is the number of edges and this equation is known as Eulers polyhedron formula. Thus the number of edges is 2 less than the sum of the numbers of vertices and faces, for example, a cube has 8 vertices and 6 faces, and hence 12 edges. In a polygon, two edges meet at each vertex, more generally, by Balinskis theorem, at least d edges meet at every vertex of a convex polytope. Similarly, in a polyhedron, exactly two faces meet at every edge, while in higher dimensional polytopes three or more two-dimensional faces meet at every edge. Thus, the edges of a polygon are its facets, the edges of a 3-dimensional convex polyhedron are its ridges, archived from the original on 4 February 2007

3. Face (geometry) – In solid geometry, a face is a flat surface that forms part of the boundary of a solid object, a three-dimensional solid bounded exclusively by flat faces is a polyhedron. In more technical treatments of the geometry of polyhedra and higher-dimensional polytopes, in elementary geometry, a face is a polygon on the boundary of a polyhedron. Other names for a polygonal face include side of a polyhedron, for example, any of the six squares that bound a cube is a face of the cube. Sometimes face is used to refer to the 2-dimensional features of a 4-polytope. With this meaning, the 4-dimensional tesseract has 24 square faces, some other polygons, which are not faces, are also important for polyhedra and tessellations. These include Petrie polygons, vertex figures and facets, any convex polyhedrons surface has Euler characteristic V − E + F =2, where V is the number of vertices, E is the number of edges, and F is the number of faces. This equation is known as Eulers polyhedron formula, thus the number of faces is 2 more than the excess of the number of edges over the number of vertices. For example, a cube has 12 edges and 8 vertices, in higher-dimensional geometry the faces of a polytope are features of all dimensions. A face of dimension k is called a k-face, for example, the polygonal faces of an ordinary polyhedron are 2-faces. In set theory, the set of faces of a polytope includes the polytope itself, for any n-polytope, −1 ≤ k ≤ n. For example, with meaning, the faces of a cube include the empty set, its vertices, edges and squares. Formally, a face of a polytope P is the intersection of P with any closed halfspace whose boundary is disjoint from the interior of P, from this definition it follows that the set of faces of a polytope includes the polytope itself and the empty set. In other areas of mathematics, such as the theories of abstract polytopes and star polytopes, abstract theory still requires that the set of faces include the polytope itself and the empty set. A cell is an element of a 4-dimensional polytope or 3-dimensional tessellation. Cells are facets for 4-polytopes and 3-honeycombs, examples, In higher-dimensional geometry, the facets of a n-polytope are the -faces of dimension one less than the polytope itself. A polytope is bounded by its facets, for example, The facets of a line segment are its 0-faces or vertices. The facets of a polygon are its 1-faces or edges, the facets of a polyhedron or plane tiling are its 2-faces. The facets of a 4D polytope or 3-honeycomb are its 3-faces, the facets of a 5D polytope or 4-honeycomb are its 4-faces

4. Cell (geometry) – In solid geometry, a face is a flat surface that forms part of the boundary of a solid object, a three-dimensional solid bounded exclusively by flat faces is a polyhedron. In more technical treatments of the geometry of polyhedra and higher-dimensional polytopes, in elementary geometry, a face is a polygon on the boundary of a polyhedron. Other names for a polygonal face include side of a polyhedron, for example, any of the six squares that bound a cube is a face of the cube. Sometimes face is used to refer to the 2-dimensional features of a 4-polytope. With this meaning, the 4-dimensional tesseract has 24 square faces, some other polygons, which are not faces, are also important for polyhedra and tessellations. These include Petrie polygons, vertex figures and facets, any convex polyhedrons surface has Euler characteristic V − E + F =2, where V is the number of vertices, E is the number of edges, and F is the number of faces. This equation is known as Eulers polyhedron formula, thus the number of faces is 2 more than the excess of the number of edges over the number of vertices. For example, a cube has 12 edges and 8 vertices, in higher-dimensional geometry the faces of a polytope are features of all dimensions. A face of dimension k is called a k-face, for example, the polygonal faces of an ordinary polyhedron are 2-faces. In set theory, the set of faces of a polytope includes the polytope itself, for any n-polytope, −1 ≤ k ≤ n. For example, with meaning, the faces of a cube include the empty set, its vertices, edges and squares. Formally, a face of a polytope P is the intersection of P with any closed halfspace whose boundary is disjoint from the interior of P, from this definition it follows that the set of faces of a polytope includes the polytope itself and the empty set. In other areas of mathematics, such as the theories of abstract polytopes and star polytopes, abstract theory still requires that the set of faces include the polytope itself and the empty set. A cell is an element of a 4-dimensional polytope or 3-dimensional tessellation. Cells are facets for 4-polytopes and 3-honeycombs, examples, In higher-dimensional geometry, the facets of a n-polytope are the -faces of dimension one less than the polytope itself. A polytope is bounded by its facets, for example, The facets of a line segment are its 0-faces or vertices. The facets of a polygon are its 1-faces or edges, the facets of a polyhedron or plane tiling are its 2-faces. The facets of a 4D polytope or 3-honeycomb are its 3-faces, the facets of a 5D polytope or 4-honeycomb are its 4-faces

5. Hypercell – In solid geometry, a face is a flat surface that forms part of the boundary of a solid object, a three-dimensional solid bounded exclusively by flat faces is a polyhedron. In more technical treatments of the geometry of polyhedra and higher-dimensional polytopes, in elementary geometry, a face is a polygon on the boundary of a polyhedron. Other names for a polygonal face include side of a polyhedron, for example, any of the six squares that bound a cube is a face of the cube. Sometimes face is used to refer to the 2-dimensional features of a 4-polytope. With this meaning, the 4-dimensional tesseract has 24 square faces, some other polygons, which are not faces, are also important for polyhedra and tessellations. These include Petrie polygons, vertex figures and facets, any convex polyhedrons surface has Euler characteristic V − E + F =2, where V is the number of vertices, E is the number of edges, and F is the number of faces. This equation is known as Eulers polyhedron formula, thus the number of faces is 2 more than the excess of the number of edges over the number of vertices. For example, a cube has 12 edges and 8 vertices, in higher-dimensional geometry the faces of a polytope are features of all dimensions. A face of dimension k is called a k-face, for example, the polygonal faces of an ordinary polyhedron are 2-faces. In set theory, the set of faces of a polytope includes the polytope itself, for any n-polytope, −1 ≤ k ≤ n. For example, with meaning, the faces of a cube include the empty set, its vertices, edges and squares. Formally, a face of a polytope P is the intersection of P with any closed halfspace whose boundary is disjoint from the interior of P, from this definition it follows that the set of faces of a polytope includes the polytope itself and the empty set. In other areas of mathematics, such as the theories of abstract polytopes and star polytopes, abstract theory still requires that the set of faces include the polytope itself and the empty set. A cell is an element of a 4-dimensional polytope or 3-dimensional tessellation. Cells are facets for 4-polytopes and 3-honeycombs, examples, In higher-dimensional geometry, the facets of a n-polytope are the -faces of dimension one less than the polytope itself. A polytope is bounded by its facets, for example, The facets of a line segment are its 0-faces or vertices. The facets of a polygon are its 1-faces or edges, the facets of a polyhedron or plane tiling are its 2-faces. The facets of a 4D polytope or 3-honeycomb are its 3-faces, the facets of a 5D polytope or 4-honeycomb are its 4-faces

6. Point (geometry) – In modern mathematics, a point refers usually to an element of some set called a space. More specifically, in Euclidean geometry, a point is a primitive notion upon which the geometry is built, being a primitive notion means that a point cannot be defined in terms of previously defined objects. That is, a point is defined only by some properties, called axioms, in particular, the geometric points do not have any length, area, volume, or any other dimensional attribute. A common interpretation is that the concept of a point is meant to capture the notion of a location in Euclidean space. Points, considered within the framework of Euclidean geometry, are one of the most fundamental objects, Euclid originally defined the point as that which has no part. This idea is easily generalized to three-dimensional Euclidean space, where a point is represented by a triplet with the additional third number representing depth. Further generalizations are represented by an ordered tuplet of n terms, many constructs within Euclidean geometry consist of an infinite collection of points that conform to certain axioms. This is usually represented by a set of points, As an example, a line is a set of points of the form L =. Similar constructions exist that define the plane, line segment and other related concepts, a line segment consisting of only a single point is called a degenerate line segment. In addition to defining points and constructs related to points, Euclid also postulated a key idea about points, in spite of this, modern expansions of the system serve to remove these assumptions. There are several inequivalent definitions of dimension in mathematics, in all of the common definitions, a point is 0-dimensional. The dimension of a space is the maximum size of a linearly independent subset. In a vector space consisting of a point, there is no linearly independent subset. The zero vector is not itself linearly independent, because there is a non trivial linear combination making it zero,1 ⋅0 =0, if no such minimal n exists, the space is said to be of infinite covering dimension. A point is zero-dimensional with respect to the covering dimension because every open cover of the space has a refinement consisting of a open set. The Hausdorff dimension of X is defined by dim H ⁡, = inf, a point has Hausdorff dimension 0 because it can be covered by a single ball of arbitrarily small radius. Although the notion of a point is considered fundamental in mainstream geometry and topology, there are some systems that forgo it, e. g. noncommutative geometry. More precisely, such structures generalize well-known spaces of functions in a way that the operation take a value at this point may not be defined

7. Line segment – In geometry, a line segment is a part of a line that is bounded by two distinct end points, and contains every point on the line between its endpoints. A closed line segment includes both endpoints, while a line segment excludes both endpoints, a half-open line segment includes exactly one of the endpoints. Examples of line include the sides of a triangle or square. More generally, when both of the end points are vertices of a polygon or polyhedron, the line segment is either an edge if they are adjacent vertices. When the end points both lie on a such as a circle, a line segment is called a chord. Sometimes one needs to distinguish between open and closed line segments, thus, the line segment can be expressed as a convex combination of the segments two end points. In geometry, it is defined that a point B is between two other points A and C, if the distance AB added to the distance BC is equal to the distance AC. Thus in R2 the line segment with endpoints A = and C = is the collection of points. A line segment is a connected, non-empty set, if V is a topological vector space, then a closed line segment is a closed set in V. However, an open line segment is an open set in V if and only if V is one-dimensional. More generally than above, the concept of a segment can be defined in an ordered geometry. A pair of segments can be any one of the following, intersecting, parallel, skew. The last possibility is a way that line segments differ from lines, in an axiomatic treatment of geometry, the notion of betweenness is either assumed to satisfy a certain number of axioms, or else be defined in terms of an isometry of a line. Segments play an important role in other theories, for example, a set is convex if the segment that joins any two points of the set is contained in the set. This is important because it transforms some of the analysis of sets to the analysis of a line segment. The Segment Addition Postulate can be used to add congruent segment or segments with equal lengths and consequently substitute other segments into another statement to make segments congruent. A line segment can be viewed as a case of an ellipse in which the semiminor axis goes to zero, the foci go to the endpoints. A complete orbit of this ellipse traverses the line segment twice, as a degenerate orbit this is a radial elliptic trajectory. In addition to appearing as the edges and diagonals of polygons and polyhedra, some very frequently considered segments in a triangle include the three altitudes, the three medians, the perpendicular bisectors of the sides, and the internal angle bisectors

8. Vertex figure – In geometry, a vertex figure, broadly speaking, is the figure exposed when a corner of a polyhedron or polytope is sliced off. Take some vertex of a polyhedron, mark a point somewhere along each connected edge. Draw lines across the faces, joining adjacent points. When done, these form a complete circuit, i. e. a polygon. This polygon is the vertex figure, more precise formal definitions can vary quite widely, according to circumstance. For example Coxeter varies his definition as convenient for the current area of discussion, most of the following definitions of a vertex figure apply equally well to infinite tilings, or space-filling tessellation with polytope cells. Make a slice through the corner of the polyhedron, cutting all the edges connected to the vertex. The cut surface is the vertex figure and this is perhaps the most common approach, and the most easily understood. Different authors make the slice in different places, Wenninger cuts each edge a unit distance from the vertex, as does Coxeter. For uniform polyhedra the Dorman Luke construction cuts each connected edge at its midpoint, other authors make the cut through the vertex at the other end of each edge. For irregular polyhedra, these approaches may produce a figure that does not lie in a plane. A more general approach, valid for convex polyhedra, is to make the cut along any plane which separates the given vertex from all the other vertices. Cromwell makes a cut or scoop, centered on the vertex. The cut surface or vertex figure is thus a spherical polygon marked on this sphere, many combinatorial and computational approaches treat a vertex figure as the ordered set of points of all the neighboring vertices to the given vertex. In the theory of polytopes, the vertex figure at a given vertex V comprises all the elements which are incident on the vertex, edges, faces. More formally it is the -section Fn/V, where Fn is the greatest face and this set of elements is elsewhere known as a vertex star. A vertex figure for an n-polytope is an -polytope, for example, a vertex figure for a polyhedron is a polygon figure, and the vertex figure for a 4-polytope is a polyhedron. Each edge of the vertex figure exists on or inside of a face of the original polytope connecting two vertices from an original face

9. Peak (geometry) – In solid geometry, a face is a flat surface that forms part of the boundary of a solid object, a three-dimensional solid bounded exclusively by flat faces is a polyhedron. In more technical treatments of the geometry of polyhedra and higher-dimensional polytopes, in elementary geometry, a face is a polygon on the boundary of a polyhedron. Other names for a polygonal face include side of a polyhedron, for example, any of the six squares that bound a cube is a face of the cube. Sometimes face is used to refer to the 2-dimensional features of a 4-polytope. With this meaning, the 4-dimensional tesseract has 24 square faces, some other polygons, which are not faces, are also important for polyhedra and tessellations. These include Petrie polygons, vertex figures and facets, any convex polyhedrons surface has Euler characteristic V − E + F =2, where V is the number of vertices, E is the number of edges, and F is the number of faces. This equation is known as Eulers polyhedron formula, thus the number of faces is 2 more than the excess of the number of edges over the number of vertices. For example, a cube has 12 edges and 8 vertices, in higher-dimensional geometry the faces of a polytope are features of all dimensions. A face of dimension k is called a k-face, for example, the polygonal faces of an ordinary polyhedron are 2-faces. In set theory, the set of faces of a polytope includes the polytope itself, for any n-polytope, −1 ≤ k ≤ n. For example, with meaning, the faces of a cube include the empty set, its vertices, edges and squares. Formally, a face of a polytope P is the intersection of P with any closed halfspace whose boundary is disjoint from the interior of P, from this definition it follows that the set of faces of a polytope includes the polytope itself and the empty set. In other areas of mathematics, such as the theories of abstract polytopes and star polytopes, abstract theory still requires that the set of faces include the polytope itself and the empty set. A cell is an element of a 4-dimensional polytope or 3-dimensional tessellation. Cells are facets for 4-polytopes and 3-honeycombs, examples, In higher-dimensional geometry, the facets of a n-polytope are the -faces of dimension one less than the polytope itself. A polytope is bounded by its facets, for example, The facets of a line segment are its 0-faces or vertices. The facets of a polygon are its 1-faces or edges, the facets of a polyhedron or plane tiling are its 2-faces. The facets of a 4D polytope or 3-honeycomb are its 3-faces, the facets of a 5D polytope or 4-honeycomb are its 4-faces

10. Ridge (geometry) – In solid geometry, a face is a flat surface that forms part of the boundary of a solid object, a three-dimensional solid bounded exclusively by flat faces is a polyhedron. In more technical treatments of the geometry of polyhedra and higher-dimensional polytopes, in elementary geometry, a face is a polygon on the boundary of a polyhedron. Other names for a polygonal face include side of a polyhedron, for example, any of the six squares that bound a cube is a face of the cube. Sometimes face is used to refer to the 2-dimensional features of a 4-polytope. With this meaning, the 4-dimensional tesseract has 24 square faces, some other polygons, which are not faces, are also important for polyhedra and tessellations. These include Petrie polygons, vertex figures and facets, any convex polyhedrons surface has Euler characteristic V − E + F =2, where V is the number of vertices, E is the number of edges, and F is the number of faces. This equation is known as Eulers polyhedron formula, thus the number of faces is 2 more than the excess of the number of edges over the number of vertices. For example, a cube has 12 edges and 8 vertices, in higher-dimensional geometry the faces of a polytope are features of all dimensions. A face of dimension k is called a k-face, for example, the polygonal faces of an ordinary polyhedron are 2-faces. In set theory, the set of faces of a polytope includes the polytope itself, for any n-polytope, −1 ≤ k ≤ n. For example, with meaning, the faces of a cube include the empty set, its vertices, edges and squares. Formally, a face of a polytope P is the intersection of P with any closed halfspace whose boundary is disjoint from the interior of P, from this definition it follows that the set of faces of a polytope includes the polytope itself and the empty set. In other areas of mathematics, such as the theories of abstract polytopes and star polytopes, abstract theory still requires that the set of faces include the polytope itself and the empty set. A cell is an element of a 4-dimensional polytope or 3-dimensional tessellation. Cells are facets for 4-polytopes and 3-honeycombs, examples, In higher-dimensional geometry, the facets of a n-polytope are the -faces of dimension one less than the polytope itself. A polytope is bounded by its facets, for example, The facets of a line segment are its 0-faces or vertices. The facets of a polygon are its 1-faces or edges, the facets of a polyhedron or plane tiling are its 2-faces. The facets of a 4D polytope or 3-honeycomb are its 3-faces, the facets of a 5D polytope or 4-honeycomb are its 4-faces

11. Polygon – In elementary geometry, a polygon /ˈpɒlɪɡɒn/ is a plane figure that is bounded by a finite chain of straight line segments closing in a loop to form a closed polygonal chain or circuit. These segments are called its edges or sides, and the points where two edges meet are the vertices or corners. The interior of the polygon is called its body. An n-gon is a polygon with n sides, for example, a polygon is a 2-dimensional example of the more general polytope in any number of dimensions. The basic geometrical notion of a polygon has been adapted in various ways to suit particular purposes, mathematicians are often concerned only with the bounding closed polygonal chain and with simple polygons which do not self-intersect, and they often define a polygon accordingly. A polygonal boundary may be allowed to intersect itself, creating star polygons and these and other generalizations of polygons are described below. The word polygon derives from the Greek adjective πολύς much, many and it has been suggested that γόνυ knee may be the origin of “gon”. Polygons are primarily classified by the number of sides, Polygons may be characterized by their convexity or type of non-convexity, Convex, any line drawn through the polygon meets its boundary exactly twice. As a consequence, all its interior angles are less than 180°, equivalently, any line segment with endpoints on the boundary passes through only interior points between its endpoints. Non-convex, a line may be found which meets its boundary more than twice, equivalently, there exists a line segment between two boundary points that passes outside the polygon. Simple, the boundary of the polygon does not cross itself, there is at least one interior angle greater than 180°. Star-shaped, the interior is visible from at least one point. The polygon must be simple, and may be convex or concave, self-intersecting, the boundary of the polygon crosses itself. Branko Grünbaum calls these coptic, though this term does not seem to be widely used, star polygon, a polygon which self-intersects in a regular way. A polygon cannot be both a star and star-shaped, equiangular, all corner angles are equal. Cyclic, all lie on a single circle, called the circumcircle. Isogonal or vertex-transitive, all lie within the same symmetry orbit. The polygon is cyclic and equiangular

12. Triangle – A triangle is a polygon with three edges and three vertices. It is one of the shapes in geometry. A triangle with vertices A, B, and C is denoted △ A B C, in Euclidean geometry any three points, when non-collinear, determine a unique triangle and a unique plane. This article is about triangles in Euclidean geometry except where otherwise noted, triangles can be classified according to the lengths of their sides, An equilateral triangle has all sides the same length. An equilateral triangle is also a polygon with all angles measuring 60°. An isosceles triangle has two sides of equal length, some mathematicians define an isosceles triangle to have exactly two equal sides, whereas others define an isosceles triangle as one with at least two equal sides. The latter definition would make all equilateral triangles isosceles triangles, the 45–45–90 right triangle, which appears in the tetrakis square tiling, is isosceles. A scalene triangle has all its sides of different lengths, equivalently, it has all angles of different measure. Hatch marks, also called tick marks, are used in diagrams of triangles, a side can be marked with a pattern of ticks, short line segments in the form of tally marks, two sides have equal lengths if they are both marked with the same pattern. In a triangle, the pattern is no more than 3 ticks. Similarly, patterns of 1,2, or 3 concentric arcs inside the angles are used to indicate equal angles, triangles can also be classified according to their internal angles, measured here in degrees. A right triangle has one of its interior angles measuring 90°, the side opposite to the right angle is the hypotenuse, the longest side of the triangle. The other two sides are called the legs or catheti of the triangle, special right triangles are right triangles with additional properties that make calculations involving them easier. One of the two most famous is the 3–4–5 right triangle, where 32 +42 =52, in this situation,3,4, and 5 are a Pythagorean triple. The other one is a triangle that has 2 angles that each measure 45 degrees. Triangles that do not have an angle measuring 90° are called oblique triangles, a triangle with all interior angles measuring less than 90° is an acute triangle or acute-angled triangle. If c is the length of the longest side, then a2 + b2 > c2, a triangle with one interior angle measuring more than 90° is an obtuse triangle or obtuse-angled triangle. If c is the length of the longest side, then a2 + b2 < c2, a triangle with an interior angle of 180° is degenerate

13. Equilateral triangle – In geometry, an equilateral triangle is a triangle in which all three sides are equal. In the familiar Euclidean geometry, equilateral triangles are also equiangular and they are regular polygons, and can therefore also be referred to as regular triangles. Thus these are properties that are unique to equilateral triangles, the three medians have equal lengths. The three angle bisectors have equal lengths, every triangle center of an equilateral triangle coincides with its centroid, which implies that the equilateral triangle is the only triangle with no Euler line connecting some of the centers. For some pairs of triangle centers, the fact that they coincide is enough to ensure that the triangle is equilateral, in particular, A triangle is equilateral if any two of the circumcenter, incenter, centroid, or orthocenter coincide. It is also equilateral if its circumcenter coincides with the Nagel point, for any triangle, the three medians partition the triangle into six smaller triangles. A triangle is equilateral if and only if any three of the triangles have either the same perimeter or the same inradius. A triangle is equilateral if and only if the circumcenters of any three of the triangles have the same distance from the centroid. Morleys trisector theorem states that, in any triangle, the three points of intersection of the adjacent angle trisectors form an equilateral triangle, a version of the isoperimetric inequality for triangles states that the triangle of greatest area among all those with a given perimeter is equilateral. That is, PA, PB, and PC satisfy the inequality that any two of them sum to at least as great as the third. By Eulers inequality, the triangle has the smallest ratio R/r of the circumradius to the inradius of any triangle, specifically. The triangle of largest area of all those inscribed in a circle is equilateral. The ratio of the area of the incircle to the area of an equilateral triangle, the ratio of the area to the square of the perimeter of an equilateral triangle,1123, is larger than that for any other triangle. If a segment splits an equilateral triangle into two regions with equal perimeters and with areas A1 and A2, then 79 ≤ A1 A2 ≤97, in no other triangle is there a point for which this ratio is as small as 2. For any point P in the plane, with p, q, and t from the vertices A, B. For any point P on the circle of an equilateral triangle, with distances p, q. There are numerous triangle inequalities that hold with equality if and only if the triangle is equilateral, an equilateral triangle is the most symmetrical triangle, having 3 lines of reflection and rotational symmetry of order 3 about its center. Its symmetry group is the group of order 6 D3

14. Isosceles triangle – In geometry, an isosceles triangle is a triangle that has two sides of equal length. By the isosceles triangle theorem, the two angles opposite the sides are themselves equal, while if the third side is different then the third angle is different. By the Steiner–Lehmus theorem, every triangle with two angle bisectors of equal length is isosceles, in an isosceles triangle that has exactly two equal sides, the equal sides are called legs and the third side is called the base. The angle included by the legs is called the vertex angle, the vertex opposite the base is called the apex. In the equilateral triangle case, since all sides are equal, any side can be called the base, if needed, and the term leg is not generally used. A triangle with two equal sides has exactly one axis of symmetry, which goes through the vertex angle. Thus the axis of symmetry coincides with the bisector of the vertex angle, the median drawn to the base, the altitude drawn from the vertex angle. Whether the isosceles triangle is acute, right or obtuse depends on the vertex angle, in Euclidean geometry, the base angles cannot be obtuse or right because their measures would sum to at least 180°, the total of all angles in any Euclidean triangle. The Euler line of any triangle goes through the orthocenter, its centroid. In an isosceles triangle with two equal sides, the Euler line coincides with the axis of symmetry. This can be seen as follows, if the vertex angle is acute, then the orthocenter, the centroid, and the circumcenter all fall inside the triangle. In an isosceles triangle the incenter lies on the Euler line, the Steiner inellipse of any triangle is the unique ellipse that is internally tangent to the triangles three sides at their midpoints. For any isosceles triangle with area T and perimeter p, we have 2 p b 3 − p 2 b 2 +16 T2 =0. By substituting the height, the formula for the area of a triangle can be derived from the general formula one-half the base times the height. This is what Herons formula reduces to in the isosceles case, if the apex angle and leg lengths of an isosceles triangle are known, then the area of that triangle is, T =2 = a 2 sin ⁡ cos ⁡. This is derived by drawing a line from the base of the triangle. The bases of two right triangles are both equal to the hypotenuse times the sine of the bisected angle by definition of the term sine. For the same reason, the heights of these triangles are equal to the times the cosine of the bisected angle

15. Scalene triangle – A triangle is a polygon with three edges and three vertices. It is one of the shapes in geometry. A triangle with vertices A, B, and C is denoted △ A B C, in Euclidean geometry any three points, when non-collinear, determine a unique triangle and a unique plane. This article is about triangles in Euclidean geometry except where otherwise noted, triangles can be classified according to the lengths of their sides, An equilateral triangle has all sides the same length. An equilateral triangle is also a polygon with all angles measuring 60°. An isosceles triangle has two sides of equal length, some mathematicians define an isosceles triangle to have exactly two equal sides, whereas others define an isosceles triangle as one with at least two equal sides. The latter definition would make all equilateral triangles isosceles triangles, the 45–45–90 right triangle, which appears in the tetrakis square tiling, is isosceles. A scalene triangle has all its sides of different lengths, equivalently, it has all angles of different measure. Hatch marks, also called tick marks, are used in diagrams of triangles, a side can be marked with a pattern of ticks, short line segments in the form of tally marks, two sides have equal lengths if they are both marked with the same pattern. In a triangle, the pattern is no more than 3 ticks. Similarly, patterns of 1,2, or 3 concentric arcs inside the angles are used to indicate equal angles, triangles can also be classified according to their internal angles, measured here in degrees. A right triangle has one of its interior angles measuring 90°, the side opposite to the right angle is the hypotenuse, the longest side of the triangle. The other two sides are called the legs or catheti of the triangle, special right triangles are right triangles with additional properties that make calculations involving them easier. One of the two most famous is the 3–4–5 right triangle, where 32 +42 =52, in this situation,3,4, and 5 are a Pythagorean triple. The other one is a triangle that has 2 angles that each measure 45 degrees. Triangles that do not have an angle measuring 90° are called oblique triangles, a triangle with all interior angles measuring less than 90° is an acute triangle or acute-angled triangle. If c is the length of the longest side, then a2 + b2 > c2, a triangle with one interior angle measuring more than 90° is an obtuse triangle or obtuse-angled triangle. If c is the length of the longest side, then a2 + b2 < c2, a triangle with an interior angle of 180° is degenerate

16. Right triangle – A right triangle or right-angled triangle is a triangle in which one angle is a right angle. The relation between the sides and angles of a triangle is the basis for trigonometry. The side opposite the angle is called the hypotenuse. The sides adjacent to the angle are called legs. Side a may be identified as the adjacent to angle B and opposed to angle A, while side b is the side adjacent to angle A. If the lengths of all three sides of a triangle are integers, the triangle is said to be a Pythagorean triangle. As with any triangle, the area is equal to one half the base multiplied by the corresponding height. In a right triangle, if one leg is taken as the then the other is height. As a formula the area T is T =12 a b where a and b are the legs of the triangle and this formula only applies to right triangles. From this, The altitude to the hypotenuse is the mean of the two segments of the hypotenuse. Each leg of the triangle is the mean proportional of the hypotenuse, in equations, f 2 = d e, b 2 = c e, a 2 = c d where a, b, c, d, e, f are as shown in the diagram. Moreover, the altitude to the hypotenuse is related to the legs of the triangle by 1 a 2 +1 b 2 =1 f 2. For solutions of this equation in integer values of a, b, f, the altitude from either leg coincides with the other leg. Since these intersect at the vertex, the right triangles orthocenter—the intersection of its three altitudes—coincides with the right-angled vertex. The Pythagorean theorem states that, In any right triangle, the area of the square whose side is the hypotenuse is equal to the sum of the areas of the squares whose sides are the two legs. This can be stated in equation form as a 2 + b 2 = c 2 where c is the length of the hypotenuse, Pythagorean triples are integer values of a, b, c satisfying this equation. The radius of the incircle of a triangle with legs a and b. The radius of the circumcircle is half the length of the hypotenuse, thus the sum of the circumradius and the inradius is half the sum of the legs, R + r = a + b 2

18. Square (geometry) – In geometry, a square is a regular quadrilateral, which means that it has four equal sides and four equal angles. It can also be defined as a rectangle in which two adjacent sides have equal length, a square with vertices ABCD would be denoted ◻ ABCD. e. A rhombus with equal diagonals a convex quadrilateral with sides a, b, c, d whose area is A =12 =12. Opposite sides of a square are both parallel and equal in length, all four angles of a square are equal. All four sides of a square are equal, the diagonals of a square are equal. The square is the n=2 case of the families of n-hypercubes and n-orthoplexes, a truncated square, t, is an octagon. An alternated square, h, is a digon, the perimeter of a square whose four sides have length ℓ is P =4 ℓ and the area A is A = ℓ2. In classical times, the power was described in terms of the area of a square. This led to the use of the square to mean raising to the second power. The area can also be calculated using the diagonal d according to A = d 22. In terms of the circumradius R, the area of a square is A =2 R2, since the area of the circle is π R2, in terms of the inradius r, the area of the square is A =4 r 2. Because it is a polygon, a square is the quadrilateral of least perimeter enclosing a given area. Dually, a square is the quadrilateral containing the largest area within a given perimeter. Indeed, if A and P are the area and perimeter enclosed by a quadrilateral, then the isoperimetric inequality holds,16 A ≤ P2 with equality if. The diagonals of a square are 2 times the length of a side of the square and this value, known as the square root of 2 or Pythagoras constant, was the first number proven to be irrational. A square can also be defined as a parallelogram with equal diagonals that bisect the angles, if a figure is both a rectangle and a rhombus, then it is a square. If a circle is circumscribed around a square, the area of the circle is π /2 times the area of the square, if a circle is inscribed in the square, the area of the circle is π /4 times the area of the square. A square has an area than any other quadrilateral with the same perimeter

20. Rhombus – In Euclidean geometry, a rhombus is a simple quadrilateral whose four sides all have the same length. Another name is equilateral quadrilateral, since equilateral means that all of its sides are equal in length, every rhombus is a parallelogram and a kite. A rhombus with right angles is a square, the word rhombus comes from Greek ῥόμβος, meaning something that spins, which derives from the verb ῥέμβω, meaning to turn round and round. The word was used both by Euclid and Archimedes, who used the term solid rhombus for two right circular cones sharing a common base, the surface we refer to as rhombus today is a cross section of this solid rhombus through the apex of each of the two cones. This is a case of the superellipse, with exponent 1. Every rhombus has two diagonals connecting pairs of vertices, and two pairs of parallel sides. Using congruent triangles, one can prove that the rhombus is symmetric across each of these diagonals and it follows that any rhombus has the following properties, Opposite angles of a rhombus have equal measure. The two diagonals of a rhombus are perpendicular, that is, a rhombus is an orthodiagonal quadrilateral, the first property implies that every rhombus is a parallelogram. Thus denoting the common side as a and the diagonals as p and q, not every parallelogram is a rhombus, though any parallelogram with perpendicular diagonals is a rhombus. In general, any quadrilateral with perpendicular diagonals, one of which is a line of symmetry, is a kite, every rhombus is a kite, and any quadrilateral that is both a kite and parallelogram is a rhombus. A rhombus is a tangential quadrilateral and that is, it has an inscribed circle that is tangent to all four sides. As for all parallelograms, the area K of a rhombus is the product of its base, the base is simply any side length a, K = a ⋅ h. The inradius, denoted by r, can be expressed in terms of the p and q as. The dual polygon of a rhombus is a rectangle, A rhombus has all sides equal, a rhombus has opposite angles equal, while a rectangle has opposite sides equal. A rhombus has a circle, while a rectangle has a circumcircle. A rhombus has an axis of symmetry through each pair of opposite vertex angles, the diagonals of a rhombus intersect at equal angles, while the diagonals of a rectangle are equal in length. The figure formed by joining the midpoints of the sides of a rhombus is a rectangle, a rhombohedron is a three-dimensional figure like a cube, except that its six faces are rhombi instead of squares. The rhombic dodecahedron is a polyhedron with 12 congruent rhombi as its faces

21. Parallelogram – In Euclidean geometry, a parallelogram is a simple quadrilateral with two pairs of parallel sides. The opposite or facing sides of a parallelogram are of equal length, by comparison, a quadrilateral with just one pair of parallel sides is a trapezoid in American English or a trapezium in British English. The three-dimensional counterpart of a parallelogram is a parallelepiped, rhomboid – A quadrilateral whose opposite sides are parallel and adjacent sides are unequal, and whose angles are not right angles Rectangle – A parallelogram with four angles of equal size. Rhombus – A parallelogram with four sides of equal length, square – A parallelogram with four sides of equal length and angles of equal size. A simple quadrilateral is a if and only if any one of the following statements is true. Two pairs of opposite angles are equal in measure, one pair of opposite sides are parallel and equal in length. Each diagonal divides the quadrilateral into two congruent triangles, the sum of the squares of the sides equals the sum of the squares of the diagonals. It has rotational symmetry of order 2, the sum of the distances from any interior point to the sides is independent of the location of the point. Thus all parallelograms have all the properties listed above, and conversely, if just one of statements is true in a simple quadrilateral. Opposite sides of a parallelogram are parallel and so will never intersect, the area of a parallelogram is twice the area of a triangle created by one of its diagonals. The area of a parallelogram is also equal to the magnitude of the cross product of two adjacent sides. Any line through the midpoint of a parallelogram bisects the area, any non-degenerate affine transformation takes a parallelogram to another parallelogram. A parallelogram has rotational symmetry of order 2, if it also has exactly two lines of reflectional symmetry then it must be a rhombus or an oblong. If it has four lines of symmetry, it is a square. The perimeter of a parallelogram is 2 where a and b are the lengths of adjacent sides, unlike any other convex polygon, a parallelogram cannot be inscribed in any triangle with less than twice its area. The centers of four squares all constructed either internally or externally on the sides of a parallelogram are the vertices of a square. If two lines parallel to sides of a parallelogram are constructed concurrent to a diagonal, then the parallelograms formed on opposite sides of that diagonal are equal in area, the diagonals of a parallelogram divide it into four triangles of equal area. All of the formulas for general convex quadrilaterals apply to parallelograms

23. Isosceles trapezoid – In Euclidean geometry, an isosceles trapezoid is a convex quadrilateral with a line of symmetry bisecting one pair of opposite sides. It is a case of a trapezoid. In any isosceles trapezoid two opposite sides are parallel, and the two sides are of equal length. The diagonals are also of equal length, the base angles of an isosceles trapezoid are equal in measure. Rectangles and squares are usually considered to be cases of isosceles trapezoids though some sources would exclude them. Another special case is a 3-equal side trapezoid, sometimes known as a trapezoid or a trisosceles trapezoid. They can also be dissected from regular polygons of 5 sides or more as a truncation of 4 sequential vertices. Any non-self-crossing quadrilateral with one axis of symmetry must be either an isosceles trapezoid or a kite. Every antiparallelogram has a trapezoid as its convex hull, and may be formed from the diagonals. The base angles have the same measure, the segment that joins the midpoints of the parallel sides is perpendicular to them. Opposite angles are supplementary, which in turn implies that isosceles trapezoids are cyclic quadrilaterals, the diagonals divide each other into segments with lengths that are pairwise equal, in terms of the picture below, AE = DE, BE = CE. In an isosceles trapezoid the base angles have the same measure pairwise, in the picture below, angles ∠ABC and ∠DCB are obtuse angles of the same measure, while angles ∠BAD and ∠CDA are acute angles, also of the same measure. Since the lines AD and BC are parallel, angles adjacent to opposite bases are supplementary, the diagonals of an isosceles trapezoid have the same length, that is, every isosceles trapezoid is an equidiagonal quadrilateral. Moreover, the diagonals divide each other in the same proportions, as pictured, the diagonals AC and BD have the same length and divide each other into segments of the same length. The ratio in each diagonal is divided is equal to the ratio of the lengths of the parallel sides that they intersect. The height is, according to the Pythagorean theorem, given by h = p 2 −2 =124 c 2 −2. The distance from point E to base AD is given by d = a h a + b where a and b are the lengths of the parallel sides AD and BC, and h is the height of the trapezoid. The area of a trapezoid is equal to the average of the lengths of the base

25. Rhomboid – Traditionally, in two-dimensional geometry, a rhomboid is a parallelogram in which adjacent sides are of unequal lengths and angles are non-right angled. A parallelogram with sides of length is a rhombus but not a rhomboid. A parallelogram with right angled corners is a rectangle but not a rhomboid, the term rhomboid is now more often used for a parallelepiped, a solid figure with six faces in which each face is a parallelogram and pairs of opposite faces lie in parallel planes. Some crystals are formed in three-dimensional rhomboids and this solid is also sometimes called a rhombic prism. The term occurs frequently in science terminology referring to both its two- and three-dimensional meaning, and let quadrilaterals other than these be called trapezia. Heath suggests that rhomboid was a term already in use. The rhomboid has no line of symmetry, but it has symmetry of order 2. In biology, rhomboid may describe a geometric rhomboid or a bilaterally-symmetrical kite-shaped or diamond-shaped outline, in a type of arthritis called pseudogout, crystals of calcium pyrophosphate dihydrate accumulate in the joint, causing inflammation. Aspiration of the joint fluid reveals rhomboid-shaped crystals under a microscope

26. Hexagon – In geometry, a hexagon is a six sided polygon or 6-gon. The total of the angles of any hexagon is 720°. A regular hexagon has Schläfli symbol and can also be constructed as an equilateral triangle, t. A regular hexagon is defined as a hexagon that is both equilateral and equiangular and it is bicentric, meaning that it is both cyclic and tangential. The common length of the sides equals the radius of the circumscribed circle, all internal angles are 120 degrees. A regular hexagon has 6 rotational symmetries and 6 reflection symmetries, the longest diagonals of a regular hexagon, connecting diametrically opposite vertices, are twice the length of one side. Like squares and equilateral triangles, regular hexagons fit together without any gaps to tile the plane, the cells of a beehive honeycomb are hexagonal for this reason and because the shape makes efficient use of space and building materials. The Voronoi diagram of a triangular lattice is the honeycomb tessellation of hexagons. It is not usually considered a triambus, although it is equilateral, the maximal diameter, D is twice the maximal radius or circumradius, R, which equals the side length, t. The minimal diameter or the diameter of the circle, d, is twice the minimal radius or inradius. If a regular hexagon has successive vertices A, B, C, D, E, F, the regular hexagon has Dih6 symmetry, order 12. There are 3 dihedral subgroups, Dih3, Dih2, and Dih1, and 4 cyclic subgroups, Z6, Z3, Z2 and these symmetries express 9 distinct symmetries of a regular hexagon. John Conway labels these by a letter and group order, r12 is full symmetry, and a1 is no symmetry. These two forms are duals of each other and have half the order of the regular hexagon. The i4 forms are regular hexagons flattened or stretched along one symmetry direction and it can be seen as an elongated rhombus, while d2 and p2 can be seen as horizontally and vertically elongated kites. G2 hexagons, with sides parallel are also called hexagonal parallelogons. Each subgroup symmetry allows one or more degrees of freedom for irregular forms, only the g6 subgroup has no degrees of freedom but can seen as directed edges. Hexagons of symmetry g2, i4, and r12, as parallelogons can tessellate the Euclidean plane by translation, other hexagon shapes can tile the plane with different orientations

27. Heptagon – In geometry, a heptagon is a seven-sided polygon or 7-gon. The heptagon is also referred to as the septagon, using sept- together with the Greek suffix -agon meaning angle. A regular heptagon, in all sides and all angles are equal, has internal angles of 5π/7 radians. The area of a regular heptagon of side length a is given by, the apothem is half the cotangent of π /7, and the area of each of the 14 small triangles is one-fourth of the apothem. This expression cannot be rewritten without complex components, since the indicated cubic function is casus irreducibilis. As 7 is a Pierpont prime but not a Fermat prime and this type of construction is called a neusis construction. It is also constructible with compass, straightedge and angle trisector, the impossibility of straightedge and compass construction follows from the observation that 2 cos ⁡2 π7 ≈1.247 is a zero of the irreducible cubic x3 + x2 − 2x −1. Consequently, this polynomial is the polynomial of 2cos, whereas the degree of the minimal polynomial for a constructible number must be a power of 2. An approximation for practical use with an error of about 0. 2% is shown in the drawing and it is attributed to Albrecht Dürer. Let A lie on the circumference of the circumcircle, then B D =12 B C gives an approximation for the edge of the heptagon. Example to illustrate the error, At a circumscribed circle radius r =1 m, since 7 is a prime number there is one subgroup with dihedral symmetry, Dih1, and 2 cyclic group symmetries, Z7, and Z1. These 4 symmetries can be seen in 4 distinct symmetries on the heptagon, john Conway labels these by a letter and group order. Full symmetry of the form is r14 and no symmetry is labeled a1. The dihedral symmetries are divided depending on whether they pass through vertices or edges, cyclic symmetries in the middle column are labeled as g for their central gyration orders. Each subgroup symmetry allows one or more degrees of freedom for irregular forms, only the g7 subgroup has no degrees of freedom but can seen as directed edges. However, no algebraic expressions with purely real terms exist for the solutions of this equation, because it is an example of casus irreducibilis. A heptagonal triangle has vertices coinciding with the first, second, and fourth vertices of a regular heptagon and angles π /7,2 π /7, thus its sides coincide with one side and two particular diagonals of the regular heptagon. Two kinds of star heptagons can be constructed from regular heptagons, labeled by Schläfli symbols, blue, and green star heptagons inside a red heptagon

28. Nonagon – In geometry, a nonagon /ˈnɒnəɡɒn/ is a nine-sided polygon or 9-gon. The name nonagon is a hybrid formation, from Latin, used equivalently, attested already in the 16th century in French nonogone. The name enneagon comes from Greek enneagonon, and is more correct. A regular nonagon is represented by Schläfli symbol and has angles of 140°. Although a regular nonagon is not constructible with compass and straightedge and it can be also constructed using neusis, or by allowing the use of an angle trisector. The following is a construction of a nonagon using a straightedge. The regular enneagon has Dih9 symmetry, order 18, there are 2 subgroup dihedral symmetries, Dih3 and Dih1, and 3 cyclic group symmetries, Z9, Z3, and Z1. These 6 symmetries can be seen in 6 distinct symmetries on the enneagon, john Conway labels these by a letter and group order. Full symmetry of the form is r18 and no symmetry is labeled a1. The dihedral symmetries are divided depending on whether they pass through vertices or edges, cyclic symmetries in the middle column are labeled as g for their central gyration orders. Each subgroup symmetry allows one or more degrees of freedom for irregular forms, only the g9 subgroup has no degrees of freedom but can seen as directed edges. The regular enneagon can tessellate the euclidean tiling with gaps and these gaps can be filled with regular hexagons and isosceles triangles. In the notation of symmetrohedron this tiling is called H with H representing *632 hexagonal symmetry in the plane, the K9 complete graph is often drawn as a regular enneagon with all 36 edges connected. This graph also represents an orthographic projection of the 9 vertices and 36 edges of the 8-simplex and they Might Be Giants have a song entitled Nonagon on their childrens album Here Come the 123s. It refers to both an attendee at a party at which everybody in the party is a many-sided polygon, slipknots logo is also a version of a nonagon, being a nine-pointed star made of three triangles. King Gizzard & the Lizard Wizard have an album titled Nonagon Infinity, temples of the Bahai Faith are required to be nonagonal. The U. S. Steel Tower is an irregular nonagon, enneagram Trisection of the angle 60°, Proximity construction Weisstein, Eric W. Nonagon

29. Decagon – In geometry, a decagon is a ten-sided polygon or 10-gon. A regular decagon has all sides of length and each internal angle will always be equal to 144°. Its Schläfli symbol is and can also be constructed as a pentagon, t. By simple trigonometry, d =2 a, and it can be written algebraically as d = a 5 +25. The side of a regular decagon inscribed in a circle is −1 +52 =1 ϕ. As 10 =2 ×5, a power of two times a Fermat prime, it follows that a regular decagon is constructible using compass and straightedge, or by an edge-bisection of a regular pentagon. An alternative method is as follows, Construct a pentagon in a circle by one of the shown in constructing a pentagon. Extend a line from each vertex of the pentagon through the center of the circle to the side of that same circle. Where each line cuts the circle is a vertex of the decagon, the five corners of the pentagon constitute alternate corners of the decagon. Join these points to the adjacent new points to form the decagon, both in the construction with given circumcircle as well as with given side length is the golden ratio dividing a line segment by exterior division the determining construction element. In the construction with given circumcircle the circular arc around G with radius GE3 produces the segment AH, a M ¯ M H ¯ = A H ¯ A M ¯ =1 +52 = Φ ≈1.618. In the construction with side length the circular arc around D with radius DA produces the segment E10F. E1 E10 ¯ E1 F ¯ = E10 F ¯ E1 E10 ¯ = R a =1 +52 = Φ ≈1.618, the regular decagon has Dih10 symmetry, order 20. There are 3 subgroup dihedral symmetries, Dih5, Dih2, and Dih1, and 4 cyclic group symmetries, Z10, Z5, Z2, and Z1. These 8 symmetries can be seen in 10 distinct symmetries on the decagon, john Conway labels these by a letter and group order. Full symmetry of the form is r20 and no symmetry is labeled a1. The dihedral symmetries are divided depending on whether they pass through vertices or edges, cyclic symmetries in the middle column are labeled as g for their central gyration orders. Each subgroup symmetry allows one or more degrees of freedom for irregular forms, only the g10 subgroup has no degrees of freedom but can seen as directed edges

30. Hendecagon – In geometry, a hendecagon or 11-gon is an eleven-sided polygon. A regular hendecagon is represented by Schläfli symbol, a regular hendecagon has internal angles of 147.27 degrees. The area of a regular hendecagon with side length a is given by A =114 a 2 cot ⁡ π11 ≃9.36564 a 2, as 11 is not a Fermat prime, the regular hendecagon is not constructible with compass and straightedge. Because 11 is not a Pierpont prime, construction of a regular hendecagon is still impossible even with the usage of an angle trisector and it can, however, be constructed via neusis construction. Close approximations to the regular hendecagon can be constructed, however, for instance, the ancient Greek mathematicians approximated the side length of a hendecagon inscribed in a unit circle as being 14/25 units long. The following construction description is given by T, the regular hendecagon has Dih11 symmetry, order 22. Since 11 is a number there is one subgroup with dihedral symmetry, Dih1, and 2 cyclic group symmetries, Z11. These 4 symmetries can be seen in 4 distinct symmetries on the hendecagon, john Conway labels these by a letter and group order. Full symmetry of the form is r22 and no symmetry is labeled a1. The dihedral symmetries are divided depending on whether they pass through vertices or edges, cyclic symmetries in the middle column are labeled as g for their central gyration orders. Each subgroup symmetry allows one or more degrees of freedom for irregular forms, only the g11 subgroup has no degrees of freedom but can seen as directed edges. The Canadian dollar coin, the loonie, is similar to, but not exactly, the cross-section of a loonie is actually a Reuleaux hendecagon. Anthony dollar has a hendecagonal outline along the inside of its edges

31. Dodecagon – In geometry, a dodecagon or 12-gon is any twelve-sided polygon. A regular dodecagon is a figure with sides of the same length. It has twelve lines of symmetry and rotational symmetry of order 12. A regular dodecagon is represented by the Schläfli symbol and can be constructed as a hexagon, t, or a twice-truncated triangle. The internal angle at each vertex of a regular dodecagon is 150°, as 12 =22 ×3, regular dodecagon is constructible using compass and straightedge, Coxeter states that every parallel-sided 2m-gon can be divided into m/2 rhombs. For the dodecagon, m=6, and it can be divided into 15 rhombs and this decomposition is based on a Petrie polygon projection of a 6-cube, with 15 of 240 faces. One of the ways the mathematical manipulative pattern blocks are used is in creating a number of different dodecagons, the regular dodecagon has Dih12 symmetry, order 24. There are 15 distinct subgroup dihedral and cyclic symmetries, each subgroup symmetry allows one or more degrees of freedom for irregular forms. Only the g12 subgroup has no degrees of freedom but can seen as directed edges, the interior of such an dodecagon is not generally defined. A skew zig-zag dodecagon has vertices alternating between two parallel planes, a regular skew dodecagon is vertex-transitive with equal edge lengths. In 3-dimensions it will be a zig-zag skew dodecagon and can be seen in the vertices and side edges of a antiprism with the same D5d, symmetry. The dodecagrammic antiprism, s and dodecagrammic crossed-antiprism, s also have regular skew dodecagons, the regular dodecagon is the Petrie polygon for many higher-dimensional polytopes, seen as orthogonal projections in Coxeter planes. Examples in 4 dimensionare the 24-cell, snub 24-cell, 6-6 duoprism, in 6 dimensions 6-cube, 6-orthoplex,221,122. It is also the Petrie polygon for the grand 120-cell and great stellated 120-cell, a dodecagram is a 12-sided star polygon, represented by symbol. There is one regular star polygon, using the same vertices, but connecting every fifth point. There are also three compounds, is reduced to 2 as two hexagons, and is reduced to 3 as three squares, is reduced to 4 as four triangles, and is reduced to 6 as six degenerate digons. Deeper truncations of the regular dodecagon and dodecagrams can produce intermediate star polygon forms with equal spaced vertices. A truncated hexagon is a dodecagon, t=, a quasitruncated hexagon, inverted as, is a dodecagram, t=

32. Triskaidecagon – In geometry, a tridecagon or triskaidecagon or 13-gon is a thirteen-sided polygon. As 13 is a Pierpont prime but not a Fermat prime, however, it is constructible using neusis, or an angle trisector. An approximate construction of a regular tridecagon using straightedge and compass is shown here, another possible animation of an approximate construction, also possible with using straightedge and compass. For details, see, Wikibooks, Tridecagon, construction description The regular tridecagon has Dih13 symmetry, since 13 is a prime number there is one subgroup with dihedral symmetry, Dih1, and 2 cyclic group symmetries, Z13, and Z1. These 4 symmetries can be seen in 4 distinct symmetries on the tridecagon, john Conway labels these by a letter and group order. Full symmetry of the form is r26 and no symmetry is labeled a1. The dihedral symmetries are divided depending on whether they pass through vertices or edges, cyclic symmetries in the middle column are labeled as g for their central gyration orders. Each subgroup symmetry allows one or more degrees of freedom for irregular forms, only the g13 subgroup has no degrees of freedom but can seen as directed edges. The regular tridecagon is used as the shape of the Czech 20 korun coin, a tridecagram is a 13-sided star polygon. There are 5 regular forms given by Schläfli symbols, and, the regular tridecagon is the Petrie polygon 12-simplex, Weisstein, Eric W. Tridecagon

39. Icosagon – In geometry, an icosagon or 20-gon is a twenty-sided polygon. The sum of any icosagons interior angles is 3240 degrees, the regular icosagon has Schläfli symbol, and can also be constructed as a truncated decagon, t, or a twice-truncated pentagon, tt. One interior angle in a regular icosagon is 162°, meaning that one exterior angle would be 18°, the area of a regular icosagon with edge length t is A =5 t 2 ≃31.5687 t 2. In terms of the radius R of its circumcircle, the area is A =5 R22, since the area of the circle is π R2, the Big Wheel on the popular US game show The Price Is Right has an icosagonal cross-section. The Globe, the outdoor theater used by William Shakespeares acting company, was discovered to have built on an icosagonal foundation when a partial excavation was done in 1989. As a golygonal path, the swastika is considered to be an irregular icosagon, a regular square, pentagon, and icosagon can completely fill a plane vertex. E20 E1 ¯ E1 F ¯ = E20 F ¯ E20 E1 ¯ =1 +52 = φ ≈1.618 The regular icosagon has Dih20 symmetry, order 40. There are 5 subgroup dihedral symmetries, and, and 6 cyclic group symmetries and these 10 symmetries can be seen in 16 distinct symmetries on the icosagon, a larger number because the lines of reflections can either pass through vertices or edges. John Conway labels these by a letter and group order, full symmetry of the regular form is r40 and no symmetry is labeled a1. The dihedral symmetries are divided depending on whether they pass through vertices or edges, cyclic symmetries in the middle column are labeled as g for their central gyration orders. Each subgroup symmetry allows one or more degrees of freedom for irregular forms, only the g20 subgroup has no degrees of freedom but can seen as directed edges. These two forms are duals of each other and have half the order of the regular icosagon. An icosagram is a 20-sided star polygon, represented by symbol, there are three regular forms given by Schläfli symbols, and. There are also five regular star figures using the vertex arrangement,2,4,5,2,4. Deeper truncations of the regular decagon and decagram can produce isogonal intermediate icosagram forms with equally spaced vertices, a regular icosagram, can be seen as a quasitruncated decagon, t=. Similarly a decagram, has a quasitruncation t=, and finally a simple truncation of a decagram gives t=

40. Icositetragon – In geometry, an icositetragon or 24-gon is a twenty-four-sided polygon. The sum of any icositetragons interior angles is 3960 degrees, the regular icositetragon is represented by Schläfli symbol and can also be constructed as a truncated dodecagon, t, or a twice-truncated hexagon, tt, or thrice-truncated triangle, ttt. One interior angle in a regular icositetragon is 165°, meaning that one exterior angle would be 15°, the area of a regular icositetragon is, A =6 t 2 cot ⁡ π24 =6 t 2. The icositetragon appeared in Archimedes polygon approximation of pi, along with the hexagon, dodecagon, tetracontaoctagon, as 24 =23 ×3, a regular icositetragon is constructible using a compass and straightedge. As a truncated dodecagon, it can be constructed by an edge-bisection of a regular dodecagon, the regular icositetragon has Dih24 symmetry, order 48. There are 7 subgroup dihedral symmetries, and, and 8 cyclic group symmetries and these 16 symmetries can be seen in 22 distinct symmetries on the icositetragon. John Conway labels these by a letter and group order, the full symmetry of the regular form is r48 and no symmetry is labeled a1. The dihedral symmetries are divided depending on whether they pass through vertices or edges, cyclic symmetries in the middle column are labeled as g for their central gyration orders. Each subgroup symmetry allows one or more degrees of freedom for irregular forms, only the g24 subgroup has no degrees of freedom but can seen as directed edges. A regular triangle, octagon, and icositetragon can completely fill a plane vertex, an icositetragram is a 24-sided star polygon. There are 3 regular forms given by Schläfli symbols, and, there are also 7 regular star figures using the same vertex arrangement,2,3,4,6,8,3, and 2. There are also isogonal icositetragrams constructed as deeper truncations of the regular dodecagon and these also generate two quasitruncations, t=, and t=. A skew icositetragon is a polygon with 24 vertices and edges. The interior of such an icositetragon is not generally defined, a skew zig-zag icositetragon has vertices alternating between two parallel planes. A regular skew icositetragon is vertex-transitive with equal edge lengths, in 3-dimensions it will be a zig-zag skew icositetragon and can be seen in the vertices and side edges of a dodecagonal antiprism with the same D12d, symmetry, order 48. The dodecagrammic antiprism, s and dodecagrammic crossed-antiprism, s also have regular skew dodecagons, the regular icositetragon is the Petrie polygon for many higher-dimensional polytopes, seen as orthogonal projections in Coxeter planes, including, Weisstein, Eric W. Icositetragon. Naming Polygons and Polyhedra polygon icosatetragon

41. List of polygons – In geometry, a polygon /ˈpɒlɪɡɒn/ is traditionally a plane figure that is bounded by a finite chain of straight line segments closing in a loop to form a closed chain or circuit. These segments are called its edges or sides, and the points where two edges meet are the vertices or corners. The word polygon comes from Late Latin polygōnum, from Greek πολύγωνον, noun use of neuter of πολύγωνος, individual polygons are named according to the number of sides, combining a Greek-derived numerical prefix with the suffix -gon, e. g. pentagon, dodecagon. The triangle, quadrilateral and nonagon are exceptions, although the regular forms trigon, tetragon, polygons are primarily named by prefixes from Greek numbers. To construct the name of a polygon with more than 20 and less than 100 edges, the kai connector is not included by some authors. Extending the system up to 999 is expressed with these prefixes, platonic solid Dice NAMING POLYGONS Benjamin Franklin Finkel, A Mathematical Solution Book Containing Systematic Solutions to Many of the Most Difficult Problems,1888

42. Triacontagon – In geometry, a triacontagon or 30-gon is a thirty-sided polygon. The sum of any triacontagons interior angles is 5040 degrees, the regular triacontagon is a constructible polygon, by an edge-bisection of a regular pentadecagon, and can also be constructed as a truncated pentadecagon, t. A truncated triacontagon, t, is a hexacontagon, one interior angle in a regular triacontagon is 168°, meaning that one exterior angle would be 12°. The regular triacontagon has Dih30 dihedral symmetry, order 60, represented by 30 lines of reflection, Dih30 has 7 dihedral subgroups, Dih15, and. It also has eight more cyclic symmetries as subgroups, and, john Conway labels these lower symmetries with a letter and order of the symmetry follows the letter. He gives d with mirror lines through vertices, p with mirror lines through edges and these lower symmetries allows degrees of freedoms in defining irregular triacontagons. Only the g30 subgroup has no degrees of freedom but can seen as directed edges, a triacontagram is a 30-sided star polygon. There are 3 regular forms given by Schläfli symbols, and, there are also isogonal triacontagrams constructed as deeper truncations of the regular pentadecagon and pentadecagram, and inverted pentadecagrams, and. Other truncations form double coverings, t==2, t==2, t==2, the regular triacontagon is the Petrie polygon for three 8-dimensional polytopes with E8 symmetry, shown in orthogonal projections in the E8 Coxeter plane. It is also the Petrie polygon for two 4-dimensional polytopes, shown in the H4 Coxeter plane, the regular triacontagram is also the Petrie polygon for the great grand stellated 120-cell and grand 600-cell

44. 257-gon – In geometry, a 257-gon is a polygon with 257 sides. The sum of the angles of any non-self-intersecting 257-gon is 91800°. The area of a regular 257-gon is A =2574 t 2 cot ⁡ π257 ≈5255.751 t 2. A whole regular 257-gon is not visually discernible from a circle, the regular 257-gon is of interest for being a constructible polygon, that is, it can be constructed using a compass and an unmarked straightedge. This is because 257 is a Fermat prime, being of the form 22n +1. Thus, the values cos ⁡ π257 and cos ⁡2 π257 are 128-degree algebraic numbers, another method involves the use of 150 circles,24 being Carlyle circles, this method is pictured below. One of these Carlyle circles solves the quadratic equation x2 + x −64 =0, the regular 257-gon has Dih257 symmetry, order 514. Since 257 is a number there is one subgroup with dihedral symmetry, Dih1, and 2 cyclic group symmetries, Z257. A 257-gram is a 257-sided star polygon, as 257 is prime, there are 127 regular forms generated by Schläfli symbols for all integers 2 ≤ n ≤128 as ⌊2572 ⌋ =128. Below is a view of, with 257 nearly radial edges, new York, Dover, p.53,1991. Benjamin Bold, Famous Problems of Geometry and How to Solve Them, new York, Dover, p.70,1982. ISBN 978-0486242972 H. S. M. Coxeter Introduction to Geometry, chapter 2, Regular polygons Leonard Eugene Dickson Constructions with Ruler and Compasses, Regular Polygons. Ch.8 in Monographs on Topics of Modern Mathematics *Relevant to the Elementary Field, new York, Dover, pp. 352–386,1955. 257-gon, approximate construction of the first side, with construction instruction

45. Chiliagon – In geometry, a chiliagon or 1000-gon is a polygon with 1000 sides. Philosophers commonly refer to chiliagons to illustrate ideas about the nature and workings of thought, meaning, a regular chiliagon is represented by Schläfli symbol and can be constructed as a truncated 500-gon, t, or a twice-truncated 250-gon, tt, or a thrice-truncated 125-gon, ttt. The measure of each internal angle in a regular chiliagon is 179. 64°, because 1000 =23 ×53, the number of sides is neither a product of distinct Fermat primes nor a power of two. Thus the regular chiliagon is not a constructible polygon, indeed, it is not even constructible with the use of neusis or an angle trisector, as the number of sides is neither a product of distinct Pierpont primes, nor a product of powers of two and three. René Descartes uses the chiliagon as an example in his Sixth Meditation to demonstrate the difference between pure intellection and imagination. He says that, when one thinks of a chiliagon, he does not imagine the thousand sides or see them as if they were present before him – as he does when one imagines a triangle, for example. The imagination constructs a confused representation, which is no different from that which it constructs of a myriagon, however, he does clearly understand what a chiliagon is, just as he understands what a triangle is, and he is able to distinguish it from a myriagon. Therefore, the intellect is not dependent on imagination, Descartes claims, as it is able to entertain clear, the example of a chiliagon is also referenced by other philosophers, such as Immanuel Kant. David Hume points out that it is impossible for the eye to determine the angles of a chiliagon to be equal to 1996 right angles, or make any conjecture, that approaches this proportion. Gottfried Leibniz comments on a use of the chiliagon by John Locke, noting that one can have an idea of the polygon without having an image of it, inspired by Descartess chiliagon example, Roderick Chisholm and other 20th-century philosophers have used similar examples to make similar points. Chisholms speckled hen, which need not have a number of speckles to be successfully imagined, is perhaps the most famous of these. The regular chiliagon has Dih1000 dihedral symmetry, order 2000, represented by 1000 lines of reflection. Dih100 has 15 dihedral subgroups, Dih500, Dih250, Dih125, Dih200, Dih100, Dih50, Dih25, Dih40, Dih20, Dih10, Dih5, Dih8, Dih4, Dih2, and Dih1. It also has 16 more cyclic symmetries as subgroups, Z1000, Z500, Z250, Z125, Z200, Z100, Z50, Z25, Z40, Z20, Z10, Z5, Z8, Z4, Z2, and Z1, with Zn representing π/n radian rotational symmetry. John Conway labels these symmetries with a letter and order of the symmetry follows the letter. He gives d with mirror lines through vertices, p with mirror lines through edges and these lower symmetries allows degrees of freedom in defining irregular chiliagons. Only the g1000 subgroup has no degrees of freedom but can seen as directed edges, a chiliagram is a 1000-sided star polygon. There are 199 regular forms given by Schläfli symbols of the form, there are also 300 regular star figures in the remaining cases

46. Myriagon – In geometry, a myriagon or 10000-gon is a polygon with 10000 sides. Several philosophers have used the regular myriagon to illustrate issues regarding thought, the measure of each internal angle in a regular myriagon is 179. 964°. The area of a regular myriagon with sides of length a is given by A =2500 a 2 cot ⁡ π10000 The result differs from the area of its circumscribed circle by up to 40 parts per billion. Because 10000 =24 ×54, the number of sides is neither a product of distinct Fermat primes nor a power of two, thus the regular myriagon is not a constructible polygon. Indeed, it is not even constructible with the use of neusis or an angle trisector, as the number of sides is neither a product of distinct Pierpont primes, the regular myriagon has Dih10000 dihedral symmetry, order 20000, represented by 10000 lines of reflection. Dih100 has 24 dihedral subgroups, and and it also has 25 more cyclic symmetries as subgroups, and, with Zn representing π/n radian rotational symmetry. John Conway labels these symmetries with a letter and order of the symmetry follows the letter. R20000 represents full symmetry, and a1 labels no symmetry and he gives d with mirror lines through vertices, p with mirror lines through edges, i with mirror lines through both vertices and edges, and g for rotational symmetry. These lower symmetries allows degrees of freedom in defining irregular myriagons, only the g10000 subgroup has no degrees of freedom but can seen as directed edges. A myriagram is an 10000-sided star polygon, there are 1999 regular forms given by Schläfli symbols of the form, where n is an integer between 2 and 5000 that is coprime to 10000. There are also 3000 regular star figures in the remaining cases

47. 65537-gon – In geometry, a 65537-gon is a polygon with 65537 sides. The sum of the angles of any non-self-intersecting 65537-gon is 11796300°. The regular 65537-gon is of interest for being a constructible polygon, that is, it can be constructed using a compass and this is because 65537 is a Fermat prime, being of the form 22n +1. Thus, the values cos ⁡ π65537 and cos ⁡2 π65537 are of a 32768-degree algebraic numbers, although it was known to Gauss by 1801 that the regular 65537-gon was constructible, the first explicit construction of a regular 65537-gon was given by Johann Gustav Hermes. The construction is complex, Hermes spent 10 years completing the 200-page manuscript. Another method involves the use of at most 1332 Carlyle circles, and this method faces practical problems, as one of these Carlyle circles solves the quadratic equation x2 + x −16384 =0. The regular 65537-gon has Dih65537 symmetry, order 131074, since 65537 is a prime number there is one subgroup with dihedral symmetry, Dih1, and 2 cyclic group symmetries, Z65537, and Z1. A 65537-gram is a 65537-sided star polygon, as 65537 is prime, there are 32767 regular forms generated by Schläfli symbols for all integers 2 ≤ n ≤32768 as ⌊655372 ⌋ =32768. New York, Dover, p.53,1991, benjamin Bold, Famous Problems of Geometry and How to Solve Them New York, Dover, p.70,1982. ISBN 978-0486242972 H. S. M. Coxeter Introduction to Geometry, chapter 2, Regular polygons Leonard Eugene Dickson Constructions with Ruler and Compasses, Regular Polygons Ch.8 in Monographs on Topics of Modern Mathematics Relevant to the Elementary Field. New York, Dover, pp. 352–386,1955, 65537-gon mathematik-olympiaden. de, with images of the documentation HERMES, retrieved on April 25,2016 Wikibooks 65573-Eck Approximate construction of the first side in two main steps

48. Megagon – A megagon or 1000000-gon is a polygon with 1 million sides. Even if drawn at the size of the Earth, a regular megagon would be difficult to distinguish from a circle. A regular megagon has an angle of 179. 99964°. The area of a regular megagon with sides of length a is given by A =250000 a 2 cot ⁡ π1000000, the perimeter of a regular megagon inscribed in the unit circle is,2000000 sin ⁡ π1000000, which is very close to 2π. In fact, for a circle the size of the Earths equator, with a circumference of 40,075 kilometres, the difference between the perimeter of the inscribed megagon and the circumference of this circle comes to less than 1/16 millimeters. Because 1000000 =26 ×56, the number of sides is not a product of distinct Fermat primes, thus the regular megagon is not a constructible polygon. Indeed, it is not even constructible with the use of neusis or an angle trisector, as the number of sides is neither a product of distinct Pierpont primes, nor a product of powers of two and three. Like René Descartes example of the chiliagon, the polygon has been used as an illustration of a well-defined concept that cannot be visualised. The megagon is also used as an illustration of the convergence of regular polygons to a circle, the regular megagon has Dih1000000 dihedral symmetry, order 2000000, represented by 1000000 lines of reflection. Dih100 has 48 dihedral subgroups, and and it also has 49 more cyclic symmetries as subgroups, and, with Zn representing π/n radian rotational symmetry. John Conway labels these symmetries with a letter and order of the symmetry follows the letter. R2000000 represents full symmetry and a1 labels no symmetry and he gives d with mirror lines through vertices, p with mirror lines through edges, i with mirror lines through both vertices and edges, and g for rotational symmetry. These lower symmetries allows degrees of freedom in defining irregular megagons, only the g1000000 subgroup has no degrees of freedom but can seen as directed edges. A megagram is a star polygon. There are 199,999 regular forms given by Schläfli symbols of the form, there are also 300,000 regular star figures in the remaining cases

49. Apeirogon – In geometry, an apeirogon is a generalized polygon with a countably infinite number of sides. It can be considered as the limit of a polygon as n approaches infinity. The interior of an apeirogon can be defined by a direction order of vertices. This article describes an apeirogon in its form as a tessellation or partition of a line. A regular apeirogon has equal edge lengths, just like any regular polygon and its Schläfli symbol is, and its Coxeter-Dynkin diagram is. It is the first in the family of regular hypercubic honeycombs. This line may be considered as a circle of radius, by analogy with regular polygons with great number of edges. In two dimensions, a regular apeirogon divides the plane into two half-planes as a regular apeirogonal dihedron, the interior of an apeirogon can be defined by its orientation, filling one half plane. Dually the apeirogonal hosohedron has digon faces and a vertex figure. A truncated apeirogonal hosohedron becomes a apeirogonal prism, with each vertex bounded by two squares and an apeirogon, an alternated apeirogonal prism is a apeirogonal antiprism, with each vertex bounded by three triangles and an apeirogon. The regular apeirogon can also be seen as linear sets within 4 of the regular, uniform tilings, an isogonal apeirogon has a single type of vertex and alternates two types of edges. A quasiregular apeirogon is an isogonal apeirogon with equal edge lengths, an isotoxal apeirogon, being the dual of an isogonal one, has one type of edge, and two types of vertices, and is therefore geometrically identical to the regular apeirogon. It can be seen by drawing vertices in alternate colors. All of these will have half the symmetry of the regular apeirogon, Regular apeirogons that are scaled to converge at infinity have the symbol and exist on horocycles, while more generally they can exist on hypercycles. The regular tiling has regular apeirogon faces, hypercyclic apeirogons can also be isogonal or quasiregular, with truncated apeirogon faces, t, like the tiling tr, with two types of edges, alternately connecting to triangles or other apeirogons. Apeirogonal tiling Apeirogonal prism Apeirogonal antiprism Apeirohedron Circle Coxeter, H. S. M. Regular Polytopes, Regular polyhedra - old and new, Aequationes Math. 16 p. 1-20 Coxeter, H. S. M. & Moser, W. O. J. Generators, archived from the original on 4 February 2007

50. Star polygon – In geometry, a star polygon is a type of non-convex polygon. Only the regular polygons have been studied in any depth. The first usage is included in polygrams which includes polygons like the pentagram, star polygon names combine a numeral prefix, such as penta-, with the Greek suffix -gram. The prefix is normally a Greek cardinal, but synonyms using other prefixes exist, for example, a nine-pointed polygon or enneagram is also known as a nonagram, using the ordinal nona from Latin. The -gram suffix derives from γραμμή meaning a line, alternatively for integers p and q, it can be considered as being constructed by connecting every qth point out of p points regularly spaced in a circular placement. A regular star polygon is denoted by its Schläfli symbol, where p and q are relatively prime, the symmetry group of is dihedral group Dn of order 2n, independent of k. A regular star polygon can also be obtained as a sequence of stellations of a regular core polygon. Regular star polygons were first studied systematically by Thomas Bradwardine, if p and q are not coprime, a degenerate polygon will result with coinciding vertices and edges. For example will appear as a triangle, but can be labeled with two sets of vertices 1-6 and this should be seen not as two overlapping triangles, but a double-winding of a single unicursal hexagon. For |n/d|, the vertices have an exterior angle, β. These polygons are often seen in tiling patterns, the parametric angle α can be chosen to match internal angles of neighboring polygons in a tessellation pattern. The interior of a polygon may be treated in different ways. Three such treatments are illustrated for a pentagram, branko Grunbaum and Geoffrey Shephard consider two of them, as regular star polygons and concave isogonal 2n-gons. These include, Where a side occurs, one side is treated as outside and this is shown in the left hand illustration and commonly occurs in computer vector graphics rendering. The number of times that the polygonal curve winds around a given region determines its density, the exterior is given a density of 0, and any region of density >0 is treated as internal. This is shown in the illustration and commonly occurs in the mathematical treatment of polyhedra. Where a line may be drawn between two sides, the region in which the line lies is treated as inside the figure and this is shown in the right hand illustration and commonly occurs when making a physical model. When the area of the polygon is calculated, each of these approaches yields a different answer, star polygons feature prominently in art and culture

51. Pentagram – A pentagram is the shape of a five-pointed star drawn with five straight strokes. The word pentagram comes from the Greek word πεντάγραμμον, from πέντε, five + γραμμή, the word pentacle is sometimes used synonymously with pentagram The word pentalpha is a learned modern revival of a post-classical Greek name of the shape. The pentagram is the simplest regular star polygon, the pentagram contains ten points and fifteen line segments. It is represented by the Schläfli symbol, like a regular pentagon, and a regular pentagon with a pentagram constructed inside it, the regular pentagram has as its symmetry group the dihedral group of order 10. The pentagram can be constructed by connecting alternate vertices of a pentagon and it can also be constructed as a stellation of a pentagon, by extending the edges of a pentagon until the lines intersect. Each intersection of edges sections the edges in the golden ratio, also, the ratio of the length of the shorter segment to the segment bounded by the two intersecting edges is φ. As the four-color illustration shows, r e d g r e e n = g r e e n b l u e = b l u e m a g e n t a = φ. The pentagram includes ten isosceles triangles, five acute and five obtuse isosceles triangles, in all of them, the ratio of the longer side to the shorter side is φ. The acute triangles are golden triangles, the obtuse isosceles triangle highlighted via the colored lines in the illustration is a golden gnomon. The pentagram of Venus is the apparent path of the planet Venus as observed from Earth, the tips of the five loops at the center of the figure have the same geometric relationship to one another as the five vertices, or points, of a pentagram. Groups of five intersections of curves, equidistant from the center, have the same geometric relationship. In early monumental Sumerian script, or cuneiform, a pentagram glyph served as a logogram for the word ub, meaning corner, angle, nook, the word Pentemychos was the title of the cosmogony of Pherecydes of Syros. Here, the five corners are where the seeds of Chronos are placed within the Earth in order for the cosmos to appear. The pentangle plays an important symbolic role in the 14th-century English poem Sir Gawain, heinrich Cornelius Agrippa and others perpetuated the popularity of the pentagram as a magic symbol, attributing the five neoplatonic elements to the five points, in typical Renaissance fashion. By the mid-19th century a distinction had developed amongst occultists regarding the pentagrams orientation. With a single point upwards it depicted spirit presiding over the four elements of matter, however, the influential writer Eliphas Levi called it evil whenever the symbol appeared the other way up. It is the goat of lust attacking the heavens with its horns and it is the sign of antagonism and fatality. It is the goat of lust attacking the heavens with its horns, faust, The pentagram thy peace doth mar

52. Hexagram – A hexagram or sexagram is a six-pointed geometric star figure with the Schläfli symbol,2, or. It is the compound of two equilateral triangles, the intersection is a regular hexagon. It is used in historical, religious and cultural contexts, for example in Hanafism, Jewish identity, in mathematics, the root system for the simple Lie group G2 is in the form of a hexagram, with six long roots and six short roots. A six-pointed star, like a hexagon, can be created using a compass. Without changing the radius of the compass, set its pivot on the circles circumference, with the pivot on the last point found, similarly find a third point on the circumference, and repeat until six such points have been marked. With a straight edge, join alternate points on the circumference to form two overlapping equilateral triangles. It is possible that as a geometric shape, like for example the triangle, circle, or square. The hexagram is a symbol called satkona yantra or sadkona yantra found on ancient South Indian Hindu temples. It symbolizes the nara-narayana, or perfect meditative state of balance achieved between Man and God, and if maintained, results in moksha, or nirvana, some researchers have theorized that the hexagram represents the astrological chart at the time of Davids birth or anointment as king. The hexagram is also known as the Kings Star in astrological circles, in antique papyri, pentagrams, together with stars and other signs, are frequently found on amulets bearing the Jewish names of God, and used to guard against fever and other diseases. Curiously the hexagram is not found among these signs, in the Greek Magical Papyri at Paris and London there are 22 signs side by side, and a circle with twelve signs, but neither a pentagram nor a hexagram. Six-pointed stars have also found in cosmological diagrams in Hinduism, Buddhism. The reasons behind this symbols common appearance in Indic religions and the West are unknown, one possibility is that they have a common origin. The other possibility is that artists and religious people from several cultures independently created the hexagram shape, within Indic lore, the shape is generally understood to consist of two triangles—one pointed up and the other down—locked in harmonious embrace. The two components are called Om and the Hrim in Sanskrit, and symbolize mans position between earth and sky, the downward triangle symbolizes Shakti, the sacred embodiment of femininity, and the upward triangle symbolizes Shiva, or Agni Tattva, representing the focused aspects of masculinity. The mystical union of the two triangles represents Creation, occurring through the union of male and female. The two locked triangles are known as Shanmukha—the six-faced, representing the six faces of Shiva & Shaktis progeny Kartikeya. This symbol is also a part of several yantras and has significance in Hindu ritual worship

53. Heptagram – A heptagram, septagram, or septogram is a seven-point star drawn with seven straight strokes. The name heptagram combines a numeral prefix, hepta-, with the Greek suffix -gram, the -gram suffix derives from γραμμῆς meaning a line. In general, a heptagram is any self-intersecting heptagon, there are two regular heptagrams, labeled as and, with the second number representing the vertex interval step from a regular heptagon. This is the smallest star polygon that can be drawn in two forms, as irreducible fractions, the two heptagrams are sometimes called the heptagram and the great heptagram. The previous one, the hexagram, is a compound of two triangles. The smallest star polygon is the pentagram, the next one is the octagram, followed by the regular enneagram, which also has two forms, and, as well as one compound of three triangles. The heptagram was used in Christianity to symbolize the seven days of creation, the heptagram is a symbol of perfection in many Christian sects. The heptagram is used in the symbol for Babalon in Thelema, the heptagram is known among neopagans as the Elven Star or Fairy Star. It is treated as a symbol in various modern pagan. Blue Star Wicca also uses the symbol, where it is referred to as a septegram, the second heptagram is a symbol of magical power in some pagan spiritualities. The heptagram is used by members of the otherkin subculture as an identifier. In alchemy, a star can refer to the seven planets which were known to ancient alchemists. The seven-pointed star is incorporated into the flags of the bands of the Cherokee Nation. The Bennington flag, a historical American Flag, has thirteen seven-pointed stars along with the numerals 76 in the canton, the Flag of Jordan contains a seven-pointed star. The Flag of Australia employs five heptagrams and one pentagram to depict the Southern Cross constellation, some old versions of the coat of arms of Georgia including the Georgian Soviet Socialist Republic used the heptagram as an element. A seven-pointed star is used as the badge in many sheriffs departments, the seven-pointed star is used as the logo for the international Danish shipping company A. P. Moller–Maersk Group, sometimes known simply as Maersk. In George R. R. Martins novel series A Song of Ice and Fire, Star polygon Stellated polygons Two-dimensional regular polytopes Bibliography Grünbaum, B. and G. C. Shephard, Tilings and Patterns, New York, W. H. Freeman & Co, polyhedra with Hollow Faces, Proc of NATO-ASI Conference on Polytopes

54. Octagram – In geometry, an octagram is an eight-angled star polygon. The name octagram combine a Greek numeral prefix, octa-, with the Greek suffix -gram, the -gram suffix derives from γραμμή meaning line. In general, an octagram is any self-intersecting octagon, the regular octagram is labeled by the Schläfli symbol, which means an 8-sided star, connected by every third point. These variations have a dihedral, Dih4, symmetry, The symbol Rub el Hizb is a Unicode glyph ۞ at U+06DE. Deeper truncations of the square can produce intermediate star polygon forms with equal spaced vertices. A truncated square is an octagon, t=, a quasitruncated square, inverted as, is an octagram, t=. The uniform star polyhedron stellated truncated hexahedron, t=t has octagram faces constructed from the cube in this way, there are two regular octagrammic star figures of the form, the first constructed as two squares =2, and second as four degenerate digons, =4. There are other isogonal and isotoxal compounds including rectangular and rhombic forms, an octagonal star can be seen as a concave hexadecagon, with internal intersecting geometry erased. It can also be dissected by radial lines, usage Rub el Hizb - Islamic character Star of Lakshmi - Indian character Auseklis – usage of regular octagram by Latvians Guñelve – representation of Venus in Mapuche iconography. Selburose – usage of regular octagram in Norwegian design Stars generally Star Stellated polygons Two-dimensional regular polytopes Grünbaum, shephard, Tilings and Patterns, New York, W. H. Freeman & Co. Polyhedra with Hollow Faces, Proc of NATO-ASI Conference on Polytopes, etc. ed T. Bisztriczky et al. John H. Conway, Heidi Burgiel, Chaim Goodman-Strass, The Symmetries of Things 2008, ISBN 978-1-56881-220-5 Weisstein, Eric W. Octagram

55. Enneagram (geometry) – In geometry, an enneagram is a nine-pointed plane figure. It is sometimes called a nonagram, the name enneagram combines the numeral prefix, ennea-, with the Greek suffix -gram. The -gram suffix derives from γραμμῆς meaning a line, a regular enneagram is constructed using the same points as the regular enneagon but connected in fixed steps. It has two forms, represented by a Schläfli symbol as and, connecting every second and every fourth points respectively, there is also a star figure, or 3, made from the regular enneagon points but connected as a compound of three equilateral triangles. This star figure is known as the star of Goliath, after or 2. The nine-pointed star or enneagram can also symbolize the nine gifts or fruits of the Holy Spirit, the heavy metal band Slipknot uses the star figure enneagram as a symbol. Nonagon List of regular star polygons Bibliography John H. Conway, Heidi Burgiel, Chaim Goodman-Strass, The Symmetries of Things 2008, ISBN 978-1-56881-220-5 Nonagram -- from Wolfram MathWorld

56. Decagram (geometry) – In geometry, a decagram is a 10-point star polygon. There is one regular decagram, containing the vertices of a regular decagon, the name decagram combine a numeral prefix, deca-, with the Greek suffix -gram. The -gram suffix derives from γραμμῆς meaning a line, for a regular decagram with unit edge lengths, the proportions of the crossing points on each edge are as shown below. Decagrams have been used as one of the motifs in girih tiles. A regular decagram is a 10-sided polygram, represented by symbol, deeper truncations of the regular pentagon and pentagram can produce intermediate star polygon forms with ten equally spaced vertices and two edge lengths that remain vertex-transitive. List of regular polytopes and compounds#Stars

57. Hendecagram – In geometry, a hendecagram is a star polygon that has eleven vertices. The name hendecagram combines a Greek numeral prefix, hendeca-, with the Greek suffix -gram, the hendeca- prefix derives from Greek ἕνδεκα meaning eleven. The -gram suffix derives from γραμμῆς meaning a line and these same four forms can also be considered as stellations of a regular hendecagon. As with all odd regular polygons and star polygons whose orders are not products of distinct Fermat primes, however, Hilton & Pedersen describe folding patterns for making the hendecagrams, and out of strips of paper. Prisms over the hendecagrams and may be used to approximate the shape of DNA molecules, fort Wood, now the base of the Statue of Liberty in New York City, is a star fort in the form of an irregular 11-point star. The Topkapı Scroll contains images of an 11-pointed star Girih form used in Islamic art, the star in this scroll is not one of the regular forms of the hendecagram, but instead uses lines that connect the vertices of a hendecagon to nearly-opposite midpoints of the hendecagons edges. 11-pointed star Girih patterns are used on the exterior of the Momine Khatun Mausoleum. An 11-point star-shaped cross-section was used in the Space Shuttle Solid Rocket Booster, hendecagrammic prism Weisstein, Eric W. Polygram

58. Dodecagram – A dodecagram is a star polygon that has 12 vertices. A regular dodecagram has the vertex arrangement as a regular dodecagon. The name dodecagram combine a numeral prefix, dodeca-, with the Greek suffix -gram, the -gram suffix derives from γραμμῆς meaning a line. A regular dodecagram can be seen as a hexagon, t=. Other isogonal variations with equal spaced vertices can be constructed with two edge lengths, there are four regular dodecagram star figures, =2, =3, =4, and =6. The first is a compound of two hexagons, the second is a compound of three squares, the third is a compound of four triangles, and the fourth is a compound of six straight-sided digons. Superimposing all the dodecagons and dodecagrams on each other – including the degenerate compound of six digons, dodecagrams can also be incorporated into uniform polyhedra. Below are the three prismatic uniform polyhedra containing regular dodecagrams, stellation Star polygon List of regular polytopes Weisstein, Eric W. Dodecagram. Shephard, Tilings and Patterns, New York, W. H. Freeman & Co, polyhedra with Hollow Faces, Proc of NATO-ASI Conference on Polytopes. Etc. ed T. Bisztriczky et al, john H. Conway, Heidi Burgiel, Chaim Goodman-Strass, The Symmetries of Things 2008, ISBN 978-1-56881-220-5

59. Concave polygon – A simple polygon that is not convex is called concave, non-convex or reentrant. A concave polygon will always have at least one reflex interior angle—that is, some lines containing interior points of a concave polygon intersect its boundary at more than two points. Some diagonals of a concave polygon lie partly or wholly outside the polygon, some sidelines of a concave polygon fail to divide the plane into two half-planes one of which entirely contains the polygon. None of these three statements holds for a convex polygon, as with any simple polygon, the sum of the internal angles of a concave polygon is π radians, equivalently 180°×, where n is the number of sides. It is always possible to partition a concave polygon into a set of convex polygons, a polynomial-time algorithm for finding a decomposition into as few convex polygons as possible is described by Chazelle & Dobkin. A triangle can never be concave, but there exist concave polygons with n sides for any n >3, an example of a concave quadrilateral is the dart. At least one interior angle does not contain all vertices in its edges. The convex hull of the polygons vertices, and that of its edges

60. Cyclic polygon – In geometry, the circumscribed circle or circumcircle of a polygon is a circle which passes through all the vertices of the polygon. The center of circle is called the circumcenter and its radius is called the circumradius. A polygon which has a circle is called a cyclic polygon. All regular simple polygons, all isosceles trapezoids, all triangles, a related notion is the one of a minimum bounding circle, which is the smallest circle that completely contains the polygon within it. All triangles are cyclic, i. e. every triangle has a circumscribed circle and this can be proven on the grounds that the general equation for a circle with center and radius r in the Cartesian coordinate system is 2 +2 = r 2. Since this equation has three parameters only three points coordinate pairs are required to determine the equation of a circle, since a triangle is defined by its three vertices, and exactly three points are required to determine a circle, every triangle can be circumscribed. The circumcenter of a triangle can be constructed by drawing any two of the three perpendicular bisectors, the center is the point where the perpendicular bisectors intersect, and the radius is the length to any of the three vertices. This is because the circumcenter is equidistant from any pair of the triangles vertices, in coastal navigation, a triangles circumcircle is sometimes used as a way of obtaining a position line using a sextant when no compass is available. The horizontal angle between two landmarks defines the circumcircle upon which the observer lies, in the Euclidean plane, it is possible to give explicitly an equation of the circumcircle in terms of the Cartesian coordinates of the vertices of the inscribed triangle. Suppose that A = B = C = are the coordinates of points A, B, using the polarization identity, these equations reduce to the condition that the matrix has a nonzero kernel. Thus the circumcircle may alternatively be described as the locus of zeros of the determinant of this matrix, a similar approach allows one to deduce the equation of the circumsphere of a tetrahedron. A unit vector perpendicular to the containing the circle is given by n ^ = × | × |. An equation for the circumcircle in trilinear coordinates x, y, z is a/x + b/y + c/z =0, an equation for the circumcircle in barycentric coordinates x, y, z is a2/x + b2/y + c2/z =0. The isogonal conjugate of the circumcircle is the line at infinity, given in coordinates by ax + by + cz =0. Additionally, the circumcircle of a triangle embedded in d dimensions can be using a generalized method. Let A, B, and C be d-dimensional points, which form the vertices of a triangle and we start by transposing the system to place C at the origin, a = A − C, b = B − C. The circumcenter, p0, is given by p 0 = ×2 ∥ a × b ∥2 + C, the Cartesian coordinates of the circumcenter are U x =1 D U y =1 D with D =2. Without loss of generality this can be expressed in a form after translation of the vertex A to the origin of the Cartesian coordinate systems

61. Regular polygon – In Euclidean geometry, a regular polygon is a polygon that is equiangular and equilateral. Regular polygons may be convex or star, in the limit, a sequence of regular polygons with an increasing number of sides becomes a circle, if the perimeter is fixed, or a regular apeirogon, if the edge length is fixed. These properties apply to all regular polygons, whether convex or star, a regular n-sided polygon has rotational symmetry of order n. All vertices of a regular polygon lie on a common circle and that is, a regular polygon is a cyclic polygon. Together with the property of equal-length sides, this implies that every regular polygon also has a circle or incircle that is tangent to every side at the midpoint. Thus a regular polygon is a tangential polygon, a regular n-sided polygon can be constructed with compass and straightedge if and only if the odd prime factors of n are distinct Fermat primes. The symmetry group of a regular polygon is dihedral group Dn, D2, D3. It consists of the rotations in Cn, together with reflection symmetry in n axes that pass through the center, if n is even then half of these axes pass through two opposite vertices, and the other half through the midpoint of opposite sides. If n is odd then all pass through a vertex. All regular simple polygons are convex and those having the same number of sides are also similar. An n-sided convex regular polygon is denoted by its Schläfli symbol, for n <3 we have two degenerate cases, Monogon, degenerate in ordinary space. Digon, a line segment, degenerate in ordinary space. In certain contexts all the polygons considered will be regular, in such circumstances it is customary to drop the prefix regular. For instance, all the faces of uniform polyhedra must be regular, for n >2 the number of diagonals is n 2, i. e.0,2,5,9. for a triangle, square, pentagon, hexagon. The diagonals divide the polygon into 1,4,11,24, for a regular n-gon inscribed in a unit-radius circle, the product of the distances from a given vertex to all other vertices equals n. For a regular simple n-gon with circumradius R and distances di from a point in the plane to the vertices. For a regular n-gon, the sum of the distances from any interior point to the n sides is n times the apothem. This is a generalization of Vivianis theorem for the n=3 case, the sum of the perpendiculars from a regular n-gons vertices to any line tangent to the circumcircle equals n times the circumradius

62. Polyform – In recreational mathematics, a polyform is a plane figure constructed by joining together identical basic polygons. The basic polygon is often a convex plane-filling polygon, such as a square or a triangle, more specific names have been given to polyforms resulting from specific basic polygons, as detailed in the table below. For example, a square basic polygon results in the well-known polyominoes, the rules for joining the polygons together may vary, and must therefore be stated for each distinct type of polyform. Generally, however, the rules apply, Two basic polygons may be joined only along a common edge. No two basic polygons may overlap, configurations of disconnected basic polygons do not qualify as polyforms. The mirror image of an asymmetric polyform is not considered a distinct polyform, polyforms can also be considered in higher dimensions. In 3-dimensional space, basic polyhedra can be joined along congruent faces, joining cubes in this way produces the polycubes. One can allow more than one basic polygon, the possibilities are so numerous that the exercise seems pointless, unless extra requirements are brought in. For example, the Penrose tiles define extra rules for joining edges, when the base form is a polygon that tiles the plane, rule 1 may be broken. For instance, squares may be joined orthogonally at vertices, as well as at edges, polyforms are a rich source of problems, puzzles and games. The basic combinatorial problem is counting the number of different polyforms, given the basic polygon and the rules, as a function of n. Polycube Polyomino Weisstein, Eric W. Polyform, the Poly Pages at RecMath. org, illustrations and information on many kinds of polyforms

63. Gnomon (figure) – Figurate numbers were a concern of Pythagorean mathematics, and Pythagoras is credited with the notion that these numbers are generated from a gnomon or basic unit. The gnomon is the piece needs to be added to a figurate number to transform it to the next bigger one. For example, the gnomon of the number is the odd number. For example, when transforming the 7-square to the 8-square, we add 15 elements, these adjunctions are the 8s in the above figure. This gnomonic technique also provides a proof that the sum of the first n odd numbers is n2, in an acute isosceles triangle, it is possible to draw a similar but smaller triangle, one of whose sides is the base of the original triangle. The gnomon of these two triangles is the triangle remaining when the smaller of the two similar isosceles triangles is removed from the larger one. Gnomon shapes are also prominent in Arithmetic Composition I, a painting by Theo van Doesburg

64. Golygon – A golygon is any polygon with all right angles whose sides are consecutive integer lengths. Golygons were invented and named by Lee Sallows, and popularized by A. K, dewdney in a 1990 Scientific American column. Variations on the definition of golygons involve allowing edges to cross, using sequences of edge lengths other than the consecutive integers, in any golygon, all horizontal edges have the same parity as each other, as do all vertical edges. Therefore, the n of sides must allow the solution of the system of equations ±1 ±3 ⋯ ± =0 ±2 ±4 ⋯ ± n =0. It follows from this that n must be a multiple of 8, the number of golygons for a given permissible value of n may be computed efficiently using generating functions. The number of golygons for permissible values of n is 4,112,8432,909288, finding the number of solutions that correspond to non-crossing golygons seems to be significantly more difficult. There is a unique eight-sided golygon, it can tile the plane by 180-degree rotation using the Conway criterion, a serial-sided isogon of order n is a closed polygon with a constant angle at each vertex and having consecutive sides of length 1,2. Golygons are a case of serial-sided isogons. The three-dimensional generalization of a golygon is called a golyhedron–a closed simply-connected solid figure confined to the faces of a cubical lattice, golyhedrons have been found with values of n equal to 32,15,12, and 11. Golygons at the On-Line Encyclopedia of Integer Sequences

65. List of uniform tilings – This table shows the 11 convex uniform tilings of the Euclidean plane, and their dual tilings. There are three regular and eight semiregular tilings in the plane, the semiregular tilings form new tilings from their duals, each made from one type of irregular face. John Conway calls the uniform duals Archimedean tilings, in parallel to the Archimedean solid polyhedra, Uniform tilings are listed by their vertex configuration, the sequence of faces that exist on each vertex. For example 4.8.8 means one square and two octagons on a vertex and these 11 uniform tilings have 32 different uniform colorings. A uniform coloring allows identical sided polygons at a vertex to be colored differently, while still maintaining vertex-uniformity, in addition to the 11 convex uniform tilings, there are also 14 nonconvex tilings, using star polygons, and reverse orientation vertex configurations. In the 1987 book, Tilings and Patterns, Branko Grünbaum calls the vertex-uniform tilings Archimedean in parallel to the Archimedean solids and their dual tilings are called Laves tilings in honor of crystallographer Fritz Laves. Theyre also called Shubnikov–Laves tilings after Shubnikov, Alekseĭ Vasilʹevich, John Conway calls the uniform duals Catalan tilings, in parallel to the Catalan solid polyhedra. The Laves tilings have vertices at the centers of the regular polygons, the tiles of the Laves tilings are called planigons. This includes the 3 regular tiles and 8 irregular ones, each vertex has edges evenly spaced around it. Three dimensional analogues of the planigons are called stereohedrons and these dual tilings are listed by their face configuration, the number of faces at each vertex of a face. For example V4.8.8 means isosceles triangle tiles with one corner with four triangles, alternated forms such as the snub can also be represented by special markups within each system. Only one uniform tiling cant be constructed by a Wythoff process, an orthogonal mirror construction also exists, seen as two sets of parallel mirrors making a rectangular fundamental domain. If the domain is square, this symmetry can be doubled by a mirror into the family. Families, B C ~2, - Symmetry of the square tiling I ~12, G ~2, - Symmetry of the regular hexagonal tiling. Uniform tilings in hyperbolic plane Percolation threshold John H. Conway, Heidi Burgiel, Chaim Goodman-Strass, The Symmetries of Things 2008, the Geometrical Foundation of Natural Structure, A Source Book of Design. Uniform edge-c-colorings of the Archimedean Tilings, Tilings by Regular polygons, Vol.50, No.5. Dale Seymour and Jill Britton, Introduction to Tessellations,1989, ISBN 978-0866514613, pp. 50–57, 71-74 Weisstein, Uniform Tessellations on the Euclid plane Tessellations of the Plane David Baileys World of Tessellations k-uniform tilings n-uniform tilings

66. Uniform tilings in hyperbolic plane – In hyperbolic geometry, a uniform hyperbolic tiling is an edge-to-edge filling of the hyperbolic plane which has regular polygons as faces and is vertex-transitive. It follows that all vertices are congruent, and the tiling has a degree of rotational and translational symmetry. Uniform tilings can be identified by their vertex configuration, a sequence of numbers representing the number of sides of the polygons around each vertex, for example 7.7.7 represents the heptagonal tiling which has 3 heptagons around each vertex. It is also regular since all the polygons are the same size, uniform tilings may be regular, quasi-regular or semi-regular. For right triangles, there are two regular tilings, represented by Schläfli symbol and, each symmetry family contains 7 uniform tilings, defined by a Wythoff symbol or Coxeter-Dynkin diagram,7 representing combinations of 3 active mirrors. An 8th represents an alternation operation, deleting alternate vertices from the highest form with all mirrors active, families with r =2 contain regular hyperbolic tilings, defined by a Coxeter group such as. Hyperbolic families with r =3 or higher are given by, hyperbolic triangles define compact uniform hyperbolic tilings. More symmetry families can be constructed from fundamental domains that are not triangles, selected families of uniform tilings are shown below. Each uniform tiling generates a dual tiling, with many of them also given below. There are infinitely many triangle group families and this article shows the regular tiling up to p, q =8, and uniform tilings in 12 families, and. The simplest set of hyperbolic tilings are regular tilings, which exist in a matrix with the regular polyhedra, the regular tiling has a dual tiling across the diagonal axis of the table. Self-dual tilings, etc. pass down the diagonal of the table, because all the elements are even, each uniform dual tiling one represents the fundamental domain of a reflective symmetry, *3333, *662, *3232, *443, *222222, *3222, and *642 respectively. As well, all 7 uniform tiling can be alternated, the triangle group, Coxeter group, orbifold contains these uniform tilings, The triangle group, Coxeter group, orbifold contains these uniform tilings. Because all the elements are even, each uniform dual tiling one represents the domain of a reflective symmetry, *4444, *882, *4242, *444, *22222222, *4222. As well, all 7 uniform tiling can be alternated, and this article shows uniform tilings in 9 families, and. The triangle group, Coxeter group, orbifold contains these uniform tilings, without right angles in the fundamental triangle, the Wythoff constructions are slightly different. For instance in the family, the snub form has six polygons around a vertex. In general the vertex figure of a tiling in a triangle is p.3. q.3. r.3

67. Archimedean tiling – Euclidean plane tilings by convex regular polygons have been widely used since antiquity. The first systematic mathematical treatment was that of Kepler in his Harmonices Mundi and this means that, for every pair of flags, there is a symmetry operation mapping the first flag to the second. This is equivalent to the tiling being an edge-to-edge tiling by congruent regular polygons, There must be six equilateral triangles, four squares or three regular hexagons at a vertex, yielding the three regular tessellations. Vertex-transitivity means that for pair of vertices there is a symmetry operation mapping the first vertex to the second. Note that there are two mirror forms of 34.6 tiling, only one of which is shown in the following table. All other regular and semiregular tilings are achiral, though these yield the same set of tilings in the plane, in other spaces there are Archimedean tilings which are not uniform. Such periodic tilings may be classified by the number of orbits of vertices, edges and tiles. If there are k orbits of vertices, a tiling is known as k -uniform or k -isogonal, if there are t orbits of tiles, as t -isohedral, if there are e orbits of edges, as e -isotoxal. K-uniform tilings with the vertex figures can be further identified by their wallpaper group symmetry. 1-uniform tilings include 3 regular tilings, and 8 semiregular ones, There are 20 2-uniform tilings,61 3-uniform tilings,151 4-uniform tilings,332 5-uniform tilings and 673 6-uniform tilings. Each can be grouped by the m of distinct vertex figures. For edge-to-edge Euclidean tilings, the angles of the polygons meeting at a vertex must add to 360 degrees. A regular n -gon has internal angle 180 degrees, only eleven of these can occur in a uniform tiling of regular polygons, given in previous sections. In particular, if three polygons meet at a vertex and one has an odd number of sides, the two polygons must be the same. If they are not, they would have to alternate around the first polygon, vertex types are listed for each. If two tilings share the two vertex types, they are given subscripts 1,2. There are 61 3-uniform tilings of the Euclidean plane,39 are 3-Archimedean with 3 distinct vertex types, while 22 have 2 identical vertex types in different symmetry orbits. Chavey There are 151 4-uniform tilings of the Euclidean plane, Brian Galebachs search reproduced Krotenheerdts list of 33 4-uniform tilings with 4 distinct vertex types, as well as finding 85 of them with 3 vertex types, and 33 with 2 vertex types

68. Square tiling – In geometry, the square tiling, square tessellation or square grid is a regular tiling of the Euclidean plane. It has Schläfli symbol of, meaning it has 4 squares around every vertex, the internal angle of the square is 90 degrees so four squares at a point make a full 360 degrees. It is one of three regular tilings of the plane, the other two are the triangular tiling and the hexagonal tiling. There are 9 distinct uniform colorings of a square tiling, naming the colors by indices on the 4 squares around a vertex,1111,1112,1112,1122,1123,1123,1212,1213,1234. Cases have simple reflection symmetry, and glide reflection symmetry, three can be seen in the same symmetry domain as reduced colorings, 1112i from 1213, 1123i from 1234, and 1112ii reduced from 1123ii. This tiling is related as a part of sequence of regular polyhedra and tilings, extending into the hyperbolic plane. Like the uniform there are eight uniform tilings that can be based from the regular square tiling. Drawing the tiles colored as red on the faces, yellow at the original vertices. However treating faces identically, there are only three distinct forms, square tiling, truncated square tiling, snub square tiling. Other quadrilateral tilings can be made with topologically equivalent to the square tiling, isohedral tilings have identical faces and vertex-transitivity, there are 17 variations, with 6 identified as triangles that do not connect edge-to-edge, or as quadrilateral with two colinear edges. Symmetry given assumes all faces are the same color, the square tiling can be used as a circle packing, placing equal diameter circles at the center of every point. Every circle is in contact with 4 other circles in the packing, the packing density is π/4=78. 54% coverage. There are 4 uniform colorings of the circle packings, there are 3 regular complex apeirogons, sharing the vertices of the square tiling. Regular complex apeirogons have vertices and edges, where edges can contain 2 or more vertices, Regular apeirogons pr are contrained by, 1/p + 2/q + 1/r =1. Edges have p vertices, and vertex figures are r-gonal, checkerboard List of regular polytopes List of uniform tilings Square lattice Tilings of regular polygons Coxeter, H. S. M. Regular Polytopes, Dover edition, ISBN 0-486-61480-8 p.296, Table II, Regular honeycombs Klitzing, 2D Euclidean tilings o4o4x - squat - O1. The Geometrical Foundation of Natural Structure, A Source Book of Design, p36 Grünbaum, Branko, and Shephard, G. C. CS1 maint, Multiple names, authors list John H. Conway, Heidi Burgiel, Chaim Goodman-Strass, The Symmetries of Things 2008, ISBN 978-1-56881-220-5 Weisstein, Eric W. Square Grid

69. Triangular tiling – In geometry, the triangular tiling or triangular tessellation is one of the three regular tilings of the Euclidean plane. Because the internal angle of the triangle is 60 degrees. The triangular tiling has Schläfli symbol of, Conway calls it a deltille, named from the triangular shape of the Greek letter delta. The triangular tiling can also be called a kishextille by a kis operation that adds a center point and it is one of three regular tilings of the plane. The other two are the square tiling and the hexagonal tiling, there are 9 distinct uniform colorings of a triangular tiling. Three of them can be derived from others by repeating colors,111212 and 111112 from 121213 by combining 1 and 3, there is one class of Archimedean colorings,111112, which is not 1-uniform, containing alternate rows of triangles where every third is colored. The example shown is 2-uniform, but there are many such Archimedean colorings that can be created by arbitrary horizontal shifts of the rows. The vertex arrangement of the tiling is called an A2 lattice. It is the 2-dimensional case of a simplectic honeycomb, the A*2 lattice can be constructed by the union of all three A2 lattices, and equivalent to the A2 lattice. + + = dual of = The vertices of the tiling are the centers of the densest possible circle packing. Every circle is in contact with 6 other circles in the packing, the packing density is  π⁄√12 or 90. 69%. Since the union of 3 A2 lattices is also an A2 lattice, the voronoi cell of a triangular tiling is a hexagon, and so the voronoi tessellation, the hexagonal tiling has a direct correspondence to the circle packings. Triangular tilings can be made with the equivalent topology as the regular tiling, with identical faces and vertex-transitivity, there are 5 variations. Symmetry given assumes all faces are the same color, the planar tilings are related to polyhedra. Putting fewer triangles on a vertex leaves a gap and allows it to be folded into a pyramid and these can be expanded to Platonic solids, five, four and three triangles on a vertex define an icosahedron, octahedron, and tetrahedron respectively. This tiling is related as a part of sequence of regular polyhedra with Schläfli symbols. It is also related as a part of sequence of Catalan solids with face configuration Vn.6.6. Like the uniform there are eight uniform tilings that can be based from the regular hexagonal tiling

70. Hexagonal tiling – In geometry, the hexagonal tiling or hexagonal tessellation is a regular tiling of the Euclidean plane, in which three hexagons meet at each vertex. It has Schläfli symbol of or t, english mathematician Conway calls it a hextille. The internal angle of the hexagon is 120 degrees so three hexagons at a point make a full 360 degrees and it is one of three regular tilings of the plane. The other two are the triangular tiling and the square tiling, the hexagonal tiling is the densest way to arrange circles in two dimensions. The Honeycomb conjecture states that the tiling is the best way to divide a surface into regions of equal area with the least total perimeter. The optimal three-dimensional structure for making honeycomb was investigated by Lord Kelvin, however, the less regular Weaire–Phelan structure is slightly better. This structure exists naturally in the form of graphite, where each sheet of graphene resembles chicken wire, tubular graphene sheets have been synthesised, these are known as carbon nanotubes. They have many applications, due to their high tensile strength. Chicken wire consists of a lattice of wires. The hexagonal tiling appears in many crystals, in three dimensions, the face-centered cubic and hexagonal close packing are common crystal structures. They are the densest known sphere packings in three dimensions, and are believed to be optimal, structurally, they comprise parallel layers of hexagonal tilings, similar to the structure of graphite. They differ in the way that the layers are staggered from each other, pure copper, amongst other materials, forms a face-centered cubic lattice. There are three distinct uniform colorings of a tiling, all generated from reflective symmetry of Wythoff constructions. The represent the periodic repeat of one colored tile, counting hexagonal distances as h first, the 3-color tiling is a tessellation generated by the order-3 permutohedrons. A chamferred hexagonal tiling replacing edges with new hexagons and transforms into another hexagonal tiling, in the limit, the original faces disappear, and the new hexagons degenerate into rhombi, and it becomes a rhombic tiling. The hexagons can be dissected into sets of 6 triangles and this is similar to the relation of the rhombic dodecahedron and the rhombo-hexagonal dodecahedron tessellations in 3 dimensions. This tiling is related to regular polyhedra with vertex figure n3. It is similarly related to the uniform truncated polyhedra with vertex figure n.6.6 and this tiling is also a part of a sequence of truncated rhombic polyhedra and tilings with Coxeter group symmetry

71. Truncated square tiling – In geometry, the truncated square tiling is a semiregular tiling by regular polygons of the Euclidean plane with one square and two octagons on each vertex. This is the only edge-to-edge tiling by regular polygons which contains an octagon. It has Schläfli symbol of t. Conway calls it a truncated quadrille, other names used for this pattern include Mediterranean tiling and octagonal tiling, which is often represented by smaller squares, and nonregular octagons which alternate long and short edges. There are 3 regular and 8 semiregular tilings in the plane, there are two distinct uniform colorings of a truncated square tiling. The truncated square tiling can be used as a packing, placing equal diameter circles at the center of every point. Every circle is in contact with 3 other circles in the packing, since there is an even number of sides of all the polygons, the circles can be alternately colored as shown below. One variations on this pattern, often called a Mediterranean pattern, is shown in stone tiles with smaller squares, other variations stretch the squares or octagons. The Pythagorean tiling alternates large and small squares, and may be seen as identical to the truncated square tiling. The squares are rotated 45 degrees and octagons are distorted into squares with mid-edge vertices, in the plane it can be represented by a compound tiling, or combined can be seen as a chamfered square tiling. Drawing the tiles colored as red on the faces, yellow at the original vertices. However treating faces identically, there are three unique topologically forms, square tiling, truncated square tiling, snub square tiling. The tetrakis square tiling is the tiling of the Euclidean plane dual to the square tiling. It can be constructed square tiling with each divided into four isosceles right triangles from the center point. Conway calls it a kisquadrille, represented by a kis operation that adds a center point and it is also called the Union Jack lattice because of the resemblance to the UK flag of the triangles surrounding its degree-8 vertices. CS1 maint, Multiple names, authors list Williams, Robert, the Geometrical Foundation of Natural Structure, A Source Book of Design. Dale Seymour and Jill Britton, Introduction to Tessellations,1989, ISBN 978-0866514613, pp. 50–56 http, //www. decrete. com/stencils/octagontile Weisstein, 2D Euclidean tilings o4x4x - tosquat - O6

72. Snub square tiling – In geometry, the snub square tiling is a semiregular tiling of the Euclidean plane. There are three triangles and two squares on each vertex and its Schläfli symbol is s. Conway calls it a snub quadrille, constructed by a snub operation applied to a square tiling. There are 3 regular and 8 semiregular tilings in the plane, there are two distinct uniform colorings of a snub square tiling. The snub square tiling can be used as a packing, placing equal diameter circles at the center of every point. Every circle is in contact with 5 other circles in the packing, the snub square tiling can be constructed as a snub operation from the square tiling, or as an alternate truncation from the truncated square tiling. An alternate truncation deletes every other vertex, creating a new faces at the removed vertices. If the original tiling is made of regular faces the new triangles will be isosceles, starting with octagons which alternate long and short edge lengths will produce a snub tiling with perfect equilateral triangle faces. Example, This tiling is related to the triangular tiling which also has 3 triangles. The snub square tiling is third in a series of snub polyhedra, 2D Euclidean tilings s4s4s - snasquat - O10. Grünbaum, Branko, and Shephard, G. C, cS1 maint, Multiple names, authors list Williams, Robert. The Geometrical Foundation of Natural Structure, A Source Book of Design, p38 Dale Seymour and Jill Britton, Introduction to Tessellations,1989, ISBN 978-0866514613, pp. 50–56, dual p.115 Weisstein, Eric W. Semiregular tessellation

73. Trihexagonal tiling – In geometry, the trihexagonal tiling is one of 11 uniform tilings of the Euclidean plane by regular polygons. It consists of triangles and regular hexagons, arranged so that each hexagon is surrounded by triangles. The name derives from the fact that it combines a hexagonal tiling. Two hexagons and two triangles alternate around each vertex, and its edges form an arrangement of lines. Its dual is the rhombille tiling and this pattern, and its place in the classification of uniform tilings, was already known to Johannes Kepler in his 1619 book Harmonices Mundi. The pattern has long used in Japanese basketry, where it is called kagome. The Japanese term for this pattern has taken up in physics. It occurs also in the structures of certain minerals. Conway calls it a hexadeltille, combining elements from a hexagonal tiling. Kagome is a traditional Japanese woven bamboo pattern, its name is composed from the words kago, meaning basket, and me, meaning eye, referring to the pattern of holes in a woven basket. It is an arrangement of laths composed of interlaced triangles such that each point where two laths cross has four neighboring points, forming the pattern of a trihexagonal tiling. The weaved process gives the Kagome a chiral wallpaper group symmetry, the term kagome lattice was coined by Japanese physicist Kôdi Husimi, and first appeared in a 1951 paper by his assistant Ichirō Shōji. The kagome lattice in this sense consists of the vertices and edges of the trihexagonal tiling, despite the name, these crossing points do not form a mathematical lattice. It is represented by the vertices and edges of the cubic honeycomb, filling space by regular tetrahedra. It contains four sets of planes of points and lines. A second expression in three dimensions has parallel layers of two dimensional lattices and is called an orthorhombic-kagome lattice, the trihexagonal prismatic honeycomb represents its edges and vertices. Some minerals, namely jarosites and herbertsmithite, contain two layers or three dimensional kagome lattice arrangement of atoms in their crystal structure. These minerals display novel physical properties connected with geometrically frustrated magnetism, for instance, the spin arrangement of the magnetic ions in Co3V2O8 rests in a kagome lattice which exhibits fascinating magnetic behavior at low temperatures

74. Truncated hexagonal tiling – In geometry, the truncated hexagonal tiling is a semiregular tiling of the Euclidean plane. There are 2 dodecagons and one triangle on each vertex and it is given an extended Schläfli symbol of t. Conway calls it a truncated hextille, constructed as a truncation operation applied to a hexagonal tiling. There are 3 regular and 8 semiregular tilings in the plane, there is only one uniform coloring of a truncated hexagonal tiling. The dodecagonal faces can be distorted into different geometries, like, Like the uniform there are eight uniform tilings that can be based from the regular hexagonal tiling. Drawing the tiles colored as red on the faces, yellow at the original vertices. This tiling is related as a part of sequence of uniform truncated polyhedra with vertex configurations. Two 2-uniform tilings are related by dissected the dodecagons into a hexagonal and 6 surrounding triangles and squares. The truncated hexagonal tiling can be used as a packing, placing equal diameter circles at the center of every point. Every circle is in contact with 3 other circles in the packing and this is the lowest density packing that can be created from a uniform tiling. The dodecagonal gaps can be filled perfectly with 7 circles, creating a denser 3-uniform packing, the triakis triangular tiling is a tiling of the Euclidean plane. It is a triangular tiling with each triangle divided into three obtuse triangles from the center point. It is labeled by face configuration V3.12.12 because each isosceles triangle face has two types of vertices, one with 3 triangles, and two with 12 triangles, Conway calls it a kisdeltille, constructed as a kis operation applied to a triangular tiling. In Japan the pattern is called asanoha for hemp leaf, although the name applies to other triakis shapes like the triakis icosahedron. It is the tessellation of the truncated hexagonal tiling which has one triangle. It is one of 7 dual uniform tilings in hexagonal symmetry, tilings of regular polygons List of uniform tilings John H. Conway, Heidi Burgiel, Chaim Goodman-Strass, The Symmetries of Things 2008, ISBN 978-1-56881-220-5 Grünbaum, Branko, and Shephard, G. C. CS1 maint, Multiple names, authors list Williams, Robert, the Geometrical Foundation of Natural Structure, A Source Book of Design. 2D Euclidean tilings o3x6x - toxat - O7

75. Rhombitrihexagonal tiling – In geometry, the rhombitrihexagonal tiling is a semiregular tiling of the Euclidean plane. There are one triangle, two squares, and one hexagon on each vertex and it has Schläfli symbol of rr. John Conway calls it a rhombihexadeltille and it can be considered a cantellated by Norman Johnsons terminology or an expanded hexagonal tiling by Alicia Boole Stotts operational language. There are 3 regular and 8 semiregular tilings in the plane, there is only one uniform coloring in a rhombitrihexagonal tiling. With edge-colorings there is a half symmetry form orbifold notation, the hexagons can be considered as truncated triangles, t with two types of edges. It has Coxeter diagram, Schläfli symbol s2, the bicolored square can be distorted into isosceles trapezoids. In the limit, where the rectangles degenerate into edges, a triangular tiling results, there is one related 2-uniform tilings, having hexagons dissected into 6 triangles. Every circle is in contact with 4 other circles in the packing, the translational lattice domain contains 6 distinct circles. The gap inside each hexagon allows for one circle, related to a 2-uniform tiling with the hexagons divided into 6 triangles, there are eight uniform tilings that can be based from the regular hexagonal tiling. Drawing the tiles colored as red on the faces, yellow at the original vertices. This tiling is related as a part of sequence of cantellated polyhedra with vertex figure. These vertex-transitive figures have reflectional symmetry, the deltoidal trihexagonal tiling is a dual of the semiregular tiling known as the rhombitrihexagonal tiling. The edges of this tiling can be formed by the overlay of the regular triangular tiling. Each kite face of this tiling has angles 120°, 90°, 60° and 90° and it is one of only eight tilings of the plane in which every edge lies on a line of symmetry of the tiling. The deltoidal trihexagonal tiling is a dual of the semiregular tiling rhombitrihexagonal tiling and its faces are deltoids or kites. It is one of 7 dual uniform tilings in hexagonal symmetry and this tiling has face transitive variations, that can distort the kites into bilateral trapezoids or more general quadrillaterals. Ignoring the face colors below, the symmetry is p6m, and the lower symmetry is p31m with 3 mirrors meeting at a point. This tiling is related to the tiling by dividing the triangles and hexagons into central triangles

76. Truncated trihexagonal tiling – In geometry, the truncated trihexagonal tiling is one of eight semiregular tilings of the Euclidean plane. There are one square, one hexagon, and one dodecagon on each vertex and it has Schläfli symbol of tr. There is only one uniform coloring of a trihexagonal tiling. A 2-uniform coloring has two colors of hexagons, 3-uniform colorings can have 3 colors of dodecagons or 3 colors of squares. The truncated trihexagonal tiling has three related 2-uniform tilings, one being a 2-uniform coloring of the semiregular rhombitrihexagonal tiling, the first dissects the hexagons into 6 triangles. The other two dissect the dodecagons into a hexagon and surrounding triangles and square, in two different orientations. The Truncated trihexagonal tiling can be used as a packing, placing equal diameter circles at the center of every point. Every circle is in contact with 3 other circles in the packing, circles can be alternatedly colored in this packing with an even number of sides of all the regular polygons of this tiling. The gap inside each hexagon allows for one circle, and each dodecagon allows for 7 circles, the kisrhombille tiling or 3-6 kisrhombille tiling is a tiling of the Euclidean plane. It is constructed by congruent 30-60 degree right triangles with 4,6, conway calls it a kisrhombille for his kis vertex bisector operation applied to the rhombille tiling. More specifically it can be called a 3-6 kisrhombille, to distinguish it from other similar hyperbolic tilings and it can be seen as an equilateral hexagonal tiling with each hexagon divided into 12 triangles from the center point. It is labeled V4.6.12 because each right triangle face has three types of vertices, one with 4 triangles, one with 6 triangles, and one with 12 triangles, the kisrhombille tiling triangles represent the fundamental domains of p6m, symmetry. There are a number of small index subgroups constructed from by mirror removal, creates *333 symmetry, shown as red mirror lines. The commutator subgroup is, which is 333 symmetry, a larger index 6 subgroup constructed as, also becomes, shown in blue mirror lines, and which has its own 333 rotational symmetry, index 12. There are eight uniform tilings that can be based from the hexagonal tiling. Drawing the tiles colored as red on the faces, yellow at the original vertices. This tiling can be considered a member of a sequence of patterns with vertex figure. For p <6, the members of the sequence are omnitruncated polyhedra, for p >6, they are tilings of the hyperbolic plane, starting with the truncated triheptagonal tiling

77. Snub hexagonal tiling – In geometry, the snub hexagonal tiling is a semiregular tiling of the Euclidean plane. There are four triangles and one hexagon on each vertex and it has Schläfli symbol of sr. The snub tetrahexagonal tiling is a hyperbolic tiling with Schläfli symbol sr. Conway calls it a snub hextille. There are 3 regular and 8 semiregular tilings in the plane and this is the only one which does not have a reflection as a symmetry. There is only one uniform coloring of a trihexagonal tiling. The snub trihexagonal tiling can be used as a packing, placing equal diameter circles at the center of every point. Every circle is in contact with 5 other circles in the packing, the lattice domain repeats 6 distinct circles. The hexagonal gaps can be filled by one circle, leading to the densest packing from the triangular tiling#circle packing. This semiregular tiling is a member of a sequence of snubbed polyhedra and tilings with vertex figure and these figures and their duals have rotational symmetry, being in the Euclidean plane for n=6, and hyperbolic plane for any higher n. The series can be considered to begin with n=2, with one set of faces degenerated into digons, in geometry, the floret pentagonal tiling or rosette pentagonal tiling is a dual semiregular tiling of the Euclidean plane. It is one of 15 known isohedral pentagon tilings and it is given its name because its six pentagonal tiles radiate out from a central point, like petals on a flower. Conway calls it a 6-fold pentille, each of its pentagonal faces has four 120° and one 60° angle. It is the dual of the tiling, snub trihexagonal tiling. The floret pentagonal tiling has geometric variations with unequal edge lengths and rotational symmetry, in one limit, an edge-length goes to zero and it becomes a deltoidal trihexagonal tiling. Tilings of regular polygons List of uniform tilings John H. Conway, Heidi Burgiel, Chaim Goodman-Strass, The Symmetries of Things 2008, ISBN 978-1-56881-220-5 Grünbaum, Branko, cS1 maint, Multiple names, authors list Williams, Robert. The Geometrical Foundation of Natural Structure, A Source Book of Design, 2D Euclidean tilings s3s6s - snathat - O11

78. Elongated triangular tiling – In geometry, the elongated triangular tiling is a semiregular tiling of the Euclidean plane. There are three triangles and two squares on each vertex and it is named as a triangular tiling elongated by rows of squares, and given Schläfli symbol, e. Conway calls it a isosnub quadrille. There are 3 regular and 8 semiregular tilings in the plane and this tiling is similar to the snub square tiling which also has 3 triangles and two squares on a vertex, but in a different order. It is also the uniform tiling that cant be created as a Wythoff construction. It can be constructed as alternate layers of apeirogonal prisms and apeirogonal antiprisms, there is one uniform colorings of an elongated triangular tiling. The 2-uniform tilings are also called Archimedean colorings, there are infinite variations of these Archimedean colorings by arbitrary shifts in the square row colorings. The elongated triangular tiling can be used as a packing, placing equal diameter circles at the center of every point. Every circle is in contact with 5 other circles in the packing and it is first in a series of symmetry mutations with hyperbolic uniform tilings with 2*n2 orbifold notation symmetry, vertex figure 4. n.4.3.3.3, and Coxeter diagram. Their duals have hexagonal faces in the plane, with face configuration V4. n.4.3.3.3. There are four related 2-uniform tilings, mixing 2 or 3 rows of triangles or squares, the prismatic pentagonal tiling is a dual uniform tiling in the Euclidean plane. It is one of 15 known isohedral pentagon tilings and it can be seen as a stretched hexagonal tiling with a set of parallel bisecting lines through the hexagons. Each of its faces has three 120° and two 90° angles. It is related to the Cairo pentagonal tiling with face configuration V3.3.4.3.4, tilings of regular polygons Elongated triangular prismatic honeycomb Gyroelongated triangular prismatic honeycomb Grünbaum, Branko, and Shephard, G. C. CS1 maint, Multiple names, authors list Williams, Robert, the Geometrical Foundation of Natural Structure, A Source Book of Design. 2D Euclidean tilings elong - etrat - O4

79. Three-dimensional space – Three-dimensional space is a geometric setting in which three values are required to determine the position of an element. This is the meaning of the term dimension. In physics and mathematics, a sequence of n numbers can be understood as a location in n-dimensional space, when n =3, the set of all such locations is called three-dimensional Euclidean space. It is commonly represented by the symbol ℝ3 and this serves as a three-parameter model of the physical universe in which all known matter exists. However, this space is one example of a large variety of spaces in three dimensions called 3-manifolds. Furthermore, in case, these three values can be labeled by any combination of three chosen from the terms width, height, depth, and breadth. In mathematics, analytic geometry describes every point in space by means of three coordinates. Three coordinate axes are given, each perpendicular to the two at the origin, the point at which they cross. They are usually labeled x, y, and z, below are images of the above-mentioned systems. Two distinct points determine a line. Three distinct points are either collinear or determine a unique plane, four distinct points can either be collinear, coplanar or determine the entire space. Two distinct lines can intersect, be parallel or be skew. Two parallel lines, or two intersecting lines, lie in a plane, so skew lines are lines that do not meet. Two distinct planes can either meet in a line or are parallel. Three distinct planes, no pair of which are parallel, can meet in a common line. In the last case, the three lines of intersection of each pair of planes are mutually parallel, a line can lie in a given plane, intersect that plane in a unique point or be parallel to the plane. In the last case, there will be lines in the plane that are parallel to the given line, a hyperplane is a subspace of one dimension less than the dimension of the full space. The hyperplanes of a space are the two-dimensional subspaces, that is

80. Regular polyhedron – A regular polyhedron is a polyhedron whose symmetry group acts transitively on its flags. A regular polyhedron is highly symmetrical, being all of edge-transitive, vertex-transitive and face-transitive, in classical contexts, many different equivalent definitions are used, a common one is that faces are congruent regular polygons which are assembled in the same way around each vertex. A regular polyhedron is identified by its Schläfli symbol of the form, there are 5 finite convex regular polyhedra, known as the Platonic solids. These are the, tetrahedron, cube, octahedron, dodecahedron and icosahedron, there are also four regular star polyhedra, making nine regular polyhedra in all. All the dihedral angles of the polyhedron are equal All the vertex figures of the polyhedron are regular polygons, All the solid angles of the polyhedron are congruent. A regular polyhedron has all of three related spheres which share its centre, An insphere, tangent to all faces, an intersphere or midsphere, tangent to all edges. A circumsphere, tangent to all vertices, the regular polyhedra are the most symmetrical of all the polyhedra. They lie in just three symmetry groups, which are named after them, Tetrahedral Octahedral Icosahedral Any shapes with icosahedral or octahedral symmetry will also contain tetrahedral symmetry, the five Platonic solids have an Euler characteristic of 2. Some of the stars have a different value. The sum of the distances from any point in the interior of a polyhedron to the sides is independent of the location of the point. However, the converse does not hold, not even for tetrahedra, in a dual pair of polyhedra, the vertices of one polyhedron correspond to the faces of the other, and vice versa. The regular polyhedra show this duality as follows, The tetrahedron is self-dual, the cube and octahedron are dual to each other. The icosahedron and dodecahedron are dual to each other, the small stellated dodecahedron and great dodecahedron are dual to each other. The great stellated dodecahedron and great icosahedron are dual to each other, the Schläfli symbol of the dual is just the original written backwards, for example the dual of is. See also Regular polytope, History of discovery, stones carved in shapes resembling clusters of spheres or knobs have been found in Scotland and may be as much as 4,000 years old. Some of these stones show not only the symmetries of the five Platonic solids, examples of these stones are on display in the John Evans room of the Ashmolean Museum at Oxford University. Why these objects were made, or how their creators gained the inspiration for them, is a mystery, the earliest known written records of the regular convex solids originated from Classical Greece. When these solids were all discovered and by whom is not known, euclids reference to Plato led to their common description as the Platonic solids

Vertex (geometry) – In geometry, a vertex is a point where two or more curves, lines, or edges meet. As a consequence of this definition, the point where two lines meet to form an angle and the corners of polygons and polyhedra are vertices. A vertex is a point of a polygon, polyhedron, or other higher-dimensional polytope. However, in theory, vertices may have fewer
1. A vertex of an angle is the endpoint where two line segments or rays come together.
Edge (geometry) – For edge in graph theory, see Edge In geometry, an edge is a particular type of line segment joining two vertices in a polygon, polyhedron, or higher-dimensional polytope. In a polygon, an edge is a segment on the boundary. In a polyhedron or more generally a polytope, an edge is a segment where two faces meet. A segment joining two vertices while
1. Three edges AB, BC, and CA, each between two vertices of a triangle.
Face (geometry) – In solid geometry, a face is a flat surface that forms part of the boundary of a solid object, a three-dimensional solid bounded exclusively by flat faces is a polyhedron. In more technical treatments of the geometry of polyhedra and higher-dimensional polytopes, in elementary geometry, a face is a polygon on the boundary of a polyhedron. Other nam
Cell (geometry) – In solid geometry, a face is a flat surface that forms part of the boundary of a solid object, a three-dimensional solid bounded exclusively by flat faces is a polyhedron. In more technical treatments of the geometry of polyhedra and higher-dimensional polytopes, in elementary geometry, a face is a polygon on the boundary of a polyhedron. Other nam
1. The cube has 3 square faces per vertex.
Hypercell – In solid geometry, a face is a flat surface that forms part of the boundary of a solid object, a three-dimensional solid bounded exclusively by flat faces is a polyhedron. In more technical treatments of the geometry of polyhedra and higher-dimensional polytopes, in elementary geometry, a face is a polygon on the boundary of a polyhedron. Other nam
1. The cube has 3 square faces per vertex.
Point (geometry) – In modern mathematics, a point refers usually to an element of some set called a space. More specifically, in Euclidean geometry, a point is a primitive notion upon which the geometry is built, being a primitive notion means that a point cannot be defined in terms of previously defined objects. That is, a point is defined only by some properties, c
1. Projecting a sphere to a plane.
Line segment – In geometry, a line segment is a part of a line that is bounded by two distinct end points, and contains every point on the line between its endpoints. A closed line segment includes both endpoints, while a line segment excludes both endpoints, a half-open line segment includes exactly one of the endpoints. Examples of line include the sides of a t
1. historical image – create a line segment (1699)
Vertex figure – In geometry, a vertex figure, broadly speaking, is the figure exposed when a corner of a polyhedron or polytope is sliced off. Take some vertex of a polyhedron, mark a point somewhere along each connected edge. Draw lines across the faces, joining adjacent points. When done, these form a complete circuit, i. e. a polygon. This polygon is the vertex
1. truncated cubic honeycomb (partial).
2. The vertex figure of a triangular prism is an isosceles triangle. The triangle face makes the short edge, and the two square faces make the long edges. A shorthand notation for this vertex figure is 3.4.4
Peak (geometry) – In solid geometry, a face is a flat surface that forms part of the boundary of a solid object, a three-dimensional solid bounded exclusively by flat faces is a polyhedron. In more technical treatments of the geometry of polyhedra and higher-dimensional polytopes, in elementary geometry, a face is a polygon on the boundary of a polyhedron. Other nam
1. The cube has 3 square faces per vertex.
Ridge (geometry) – In solid geometry, a face is a flat surface that forms part of the boundary of a solid object, a three-dimensional solid bounded exclusively by flat faces is a polyhedron. In more technical treatments of the geometry of polyhedra and higher-dimensional polytopes, in elementary geometry, a face is a polygon on the boundary of a polyhedron. Other nam
1. The cube has 3 square faces per vertex.
Polygon – In elementary geometry, a polygon /ˈpɒlɪɡɒn/ is a plane figure that is bounded by a finite chain of straight line segments closing in a loop to form a closed polygonal chain or circuit. These segments are called its edges or sides, and the points where two edges meet are the vertices or corners. The interior of the polygon is called its body. An n-
1. Historical image of polygons (1699)
2. Some different types of polygon
3. The Giant's Causeway, in Northern Ireland
Triangle – A triangle is a polygon with three edges and three vertices. It is one of the shapes in geometry. A triangle with vertices A, B, and C is denoted △ A B C, in Euclidean geometry any three points, when non-collinear, determine a unique triangle and a unique plane. This article is about triangles in Euclidean geometry except where otherwise noted, tri
1. The Flatiron Building in New York is shaped like a triangular prism
2. A triangle
Equilateral triangle – In geometry, an equilateral triangle is a triangle in which all three sides are equal. In the familiar Euclidean geometry, equilateral triangles are also equiangular and they are regular polygons, and can therefore also be referred to as regular triangles. Thus these are properties that are unique to equilateral triangles, the three medians have eq
1. A regular tetrahedron is made of four equilateral triangles.
2. Equilateral triangle
Isosceles triangle – In geometry, an isosceles triangle is a triangle that has two sides of equal length. By the isosceles triangle theorem, the two angles opposite the sides are themselves equal, while if the third side is different then the third angle is different. By the Steiner–Lehmus theorem, every triangle with two angle bisectors of equal length is isosceles, i
1. The Flatiron Building in New York is shaped like a triangular prism
Scalene triangle – A triangle is a polygon with three edges and three vertices. It is one of the shapes in geometry. A triangle with vertices A, B, and C is denoted △ A B C, in Euclidean geometry any three points, when non-collinear, determine a unique triangle and a unique plane. This article is about triangles in Euclidean geometry except where otherwise noted, tri
1. The Flatiron Building in New York is shaped like a triangular prism
2. A triangle
Right triangle – A right triangle or right-angled triangle is a triangle in which one angle is a right angle. The relation between the sides and angles of a triangle is the basis for trigonometry. The side opposite the angle is called the hypotenuse. The sides adjacent to the angle are called legs. Side a may be identified as the adjacent to angle B and opposed to
1. Right triangle
Quadrilateral – In Euclidean plane geometry, a quadrilateral is a polygon with four edges and four vertices or corners. Sometimes, the quadrangle is used, by analogy with triangle. The origin of the quadrilateral is the two Latin words quadri, a variant of four, and latus, meaning side. Quadrilaterals are simple or complex, also called crossed, simple quadrilatera
1. Six different types of quadrilaterals
Square (geometry) – In geometry, a square is a regular quadrilateral, which means that it has four equal sides and four equal angles. It can also be defined as a rectangle in which two adjacent sides have equal length, a square with vertices ABCD would be denoted ◻ ABCD. e. A rhombus with equal diagonals a convex quadrilateral with sides a, b, c, d whose area is A =12
Rectangle – In Euclidean plane geometry, a rectangle is a quadrilateral with four right angles. It can also be defined as a quadrilateral, since equiangular means that all of its angles are equal. It can also be defined as a parallelogram containing a right angle, a rectangle with four sides of equal length is a square. The term oblong is occasionally used to
1. Running bond
2. Rectangle
Rhombus – In Euclidean geometry, a rhombus is a simple quadrilateral whose four sides all have the same length. Another name is equilateral quadrilateral, since equilateral means that all of its sides are equal in length, every rhombus is a parallelogram and a kite. A rhombus with right angles is a square, the word rhombus comes from Greek ῥόμβος, meaning so
1. Some polyhedra with all rhombic faces
2. Two rhombi.
Parallelogram – In Euclidean geometry, a parallelogram is a simple quadrilateral with two pairs of parallel sides. The opposite or facing sides of a parallelogram are of equal length, by comparison, a quadrilateral with just one pair of parallel sides is a trapezoid in American English or a trapezium in British English. The three-dimensional counterpart of a paral
1. This parallelogram is a rhomboid as it has no right angles and unequal sides.
Trapezoid – The parallel sides are called the bases of the trapezoid and the other two sides are called the legs or the lateral sides. A scalene trapezoid is a trapezoid with no sides of equal measure, the first recorded use of the Greek word translated trapezoid was by Marinus Proclus in his Commentary on the first book of Euclids Elements. This article uses
1. The Temple of Dendur in the Metropolitan Museum of Art in New York City
2. Trapezoid
3. Example of a trapeziform pronotum outlined on a spurge bug
Isosceles trapezoid – In Euclidean geometry, an isosceles trapezoid is a convex quadrilateral with a line of symmetry bisecting one pair of opposite sides. It is a case of a trapezoid. In any isosceles trapezoid two opposite sides are parallel, and the two sides are of equal length. The diagonals are also of equal length, the base angles of an isosceles trapezoid are eq
1. Isosceles trapezoid with axis of symmetry
Kite (geometry) – In Euclidean geometry, a kite is a quadrilateral whose four sides can be grouped into two pairs of equal-length sides that are adjacent to each other. In contrast, a parallelogram also has two pairs of sides, but they are opposite to each other rather than adjacent. Kite quadrilaterals are named for the wind-blown, flying kites, which often have th
1. V4.3.4.3
2. A kite showing its sides equal in length and its inscribed circle.
3. V4.3.4.4
4. V4.3.4.5
Rhomboid – Traditionally, in two-dimensional geometry, a rhomboid is a parallelogram in which adjacent sides are of unequal lengths and angles are non-right angled. A parallelogram with sides of length is a rhombus but not a rhomboid. A parallelogram with right angled corners is a rectangle but not a rhomboid, the term rhomboid is now more often used for a pa
1. These shapes are rhomboids
Hexagon – In geometry, a hexagon is a six sided polygon or 6-gon. The total of the angles of any hexagon is 720°. A regular hexagon has Schläfli symbol and can also be constructed as an equilateral triangle, t. A regular hexagon is defined as a hexagon that is both equilateral and equiangular and it is bicentric, meaning that it is both cyclic and tangential
1. Giants causeway closeup
2. The ideal crystalline structure of graphene is a hexagonal grid.
3. Assembled E-ELT mirror segments
4. A beehive honeycomb
Heptagon – In geometry, a heptagon is a seven-sided polygon or 7-gon. The heptagon is also referred to as the septagon, using sept- together with the Greek suffix -agon meaning angle. A regular heptagon, in all sides and all angles are equal, has internal angles of 5π/7 radians. The area of a regular heptagon of side length a is given by, the apothem is half
1. Cactus
2. A regular heptagon
Nonagon – In geometry, a nonagon /ˈnɒnəɡɒn/ is a nine-sided polygon or 9-gon. The name nonagon is a hybrid formation, from Latin, used equivalently, attested already in the 16th century in French nonogone. The name enneagon comes from Greek enneagonon, and is more correct. A regular nonagon is represented by Schläfli symbol and has angles of 140°. Although a
1. A regular nonagon (enneagon)
Decagon – In geometry, a decagon is a ten-sided polygon or 10-gon. A regular decagon has all sides of length and each internal angle will always be equal to 144°. Its Schläfli symbol is and can also be constructed as a pentagon, t. By simple trigonometry, d =2 a, and it can be written algebraically as d = a 5 +25. The side of a regular decagon inscribed in a
1. A regular decagon
Hendecagon – In geometry, a hendecagon or 11-gon is an eleven-sided polygon. A regular hendecagon is represented by Schläfli symbol, a regular hendecagon has internal angles of 147.27 degrees. The area of a regular hendecagon with side length a is given by A =114 a 2 cot ⁡ π11 ≃9.36564 a 2, as 11 is not a Fermat prime, the regular hendecagon is not constructibl
1. A regular hendecagon
Dodecagon – In geometry, a dodecagon or 12-gon is any twelve-sided polygon. A regular dodecagon is a figure with sides of the same length. It has twelve lines of symmetry and rotational symmetry of order 12. A regular dodecagon is represented by the Schläfli symbol and can be constructed as a hexagon, t, or a twice-truncated triangle. The internal angle at eac
1. pattern blocks
2. A regular dodecagon
3. The Vera Cruz church in Segovia
4. A 1942 British threepence, reverse
Triskaidecagon – In geometry, a tridecagon or triskaidecagon or 13-gon is a thirteen-sided polygon. As 13 is a Pierpont prime but not a Fermat prime, however, it is constructible using neusis, or an angle trisector. An approximate construction of a regular tridecagon using straightedge and compass is shown here, another possible animation of an approximate construc
1. A regular tridecagon
Tetradecagon – In geometry, a tetradecagon or tetrakaidecagon or 14-gon is a fourteen-sided polygon. A regular tetradecagon has Schläfli symbol and can be constructed as a quasiregular truncated heptagon, t, however, it is constructible using neusis, as for example in the following illustration with use of the angle trisector. Based on the circle r =1 Constructed
Pentadecagon – In geometry, a pentadecagon or pentakaidecagon or 15-gon is a fifteen-sided polygon. A regular pentadecagon is represented by Schläfli symbol, a regular pentadecagon has interior angles of 156°, and with a side length a, has an area given by A =154 a 2 cot ⁡ π15 =15 a 28 ≃17.6424 a 2. A regular triangle, decagon, and pentadecagon can completely fil
Hexadecagon – In mathematics, a hexadecagon or 16-gon is a sixteen-sided polygon. A regular hexadecagon is a hexadecagon in which all angles are equal and its Schläfli symbol is and can be constructed as a truncated octagon, t, and a twice-truncated square tt. A truncated hexadecagon, t, is a triacontadigon, as 16 =24, a regular hexadecagon is constructible usin
1. The hexadecagonal tower from Raphael's The Marriage of the Virgin
3. A hexadecagrammic pattern from the Alhambra
Heptadecagon – In geometry, a heptadecagon or 17-gon is a seventeen-sided polygon. A regular heptadecagon is represented by the Schläfli symbol, as 17 is a Fermat prime, the regular heptadecagon is a constructible polygon, this was shown by Carl Friedrich Gauss in 1796 at the age of 19. This proof represented the first progress in regular polygon construction in
Octadecagon – An octadecagon or 18-gon is an eighteen-sided polygon. A regular octadecagon has a Schläfli symbol and can be constructed as a truncated enneagon, t. As 18 =2 ×32, a regular octadecagon cannot be constructed using a compass, however, it is constructible using neusis, or an angle trisection with a tomahawk. The following approximate construction is
Enneadecagon – In geometry an enneadecagon or 19-gon is a nineteen-sided polygon. It is also known as an enneakaidecagon or a nonadecagon, a regular enneadecagon is represented by Schläfli symbol. The radius of the circumcircle of the regular enneadecagon with side length t is R = t 2 csc ⁡18019, the area, where t is the edge length, is 194 t 2 cot ⁡ π19 ≃28.4652
Icosagon – In geometry, an icosagon or 20-gon is a twenty-sided polygon. The sum of any icosagons interior angles is 3240 degrees, the regular icosagon has Schläfli symbol, and can also be constructed as a truncated decagon, t, or a twice-truncated pentagon, tt. One interior angle in a regular icosagon is 162°, meaning that one exterior angle would be 18°, th
1. A regular icosagon
Icositetragon – In geometry, an icositetragon or 24-gon is a twenty-four-sided polygon. The sum of any icositetragons interior angles is 3960 degrees, the regular icositetragon is represented by Schläfli symbol and can also be constructed as a truncated dodecagon, t, or a twice-truncated hexagon, tt, or thrice-truncated triangle, ttt. One interior angle in a regul
1. A regular icositetragon
List of polygons – In geometry, a polygon /ˈpɒlɪɡɒn/ is traditionally a plane figure that is bounded by a finite chain of straight line segments closing in a loop to form a closed chain or circuit. These segments are called its edges or sides, and the points where two edges meet are the vertices or corners. The word polygon comes from Late Latin polygōnum, from Greek
1. A pentagon is a five sided polygon. A regular pentagon has 5 equal edges and 5 equal angles.
Triacontagon – In geometry, a triacontagon or 30-gon is a thirty-sided polygon. The sum of any triacontagons interior angles is 5040 degrees, the regular triacontagon is a constructible polygon, by an edge-bisection of a regular pentadecagon, and can also be constructed as a truncated pentadecagon, t. A truncated triacontagon, t, is a hexacontagon, one interior a
1. A regular triacontagon
Tetracontagon – In geometry, a tetracontagon or tessaracontagon is a forty-sided polygon or 40-gon. The sum of any tetracontagons interior angles is 6840 degrees, a regular tetracontagon is represented by Schläfli symbol and can also be constructed as a truncated icosagon, t, which alternates two types of edges. Furthermore, it can also be constructed as a twice-t
1. A regular tetracontagon
257-gon – In geometry, a 257-gon is a polygon with 257 sides. The sum of the angles of any non-self-intersecting 257-gon is 91800°. The area of a regular 257-gon is A =2574 t 2 cot ⁡ π257 ≈5255.751 t 2. A whole regular 257-gon is not visually discernible from a circle, the regular 257-gon is of interest for being a constructible polygon, that is, it can be c
1. A regular 257-gon
Chiliagon – In geometry, a chiliagon or 1000-gon is a polygon with 1000 sides. Philosophers commonly refer to chiliagons to illustrate ideas about the nature and workings of thought, meaning, a regular chiliagon is represented by Schläfli symbol and can be constructed as a truncated 500-gon, t, or a twice-truncated 250-gon, tt, or a thrice-truncated 125-gon, t
1. A regular chiliagon
Myriagon – In geometry, a myriagon or 10000-gon is a polygon with 10000 sides. Several philosophers have used the regular myriagon to illustrate issues regarding thought, the measure of each internal angle in a regular myriagon is 179. 964°. The area of a regular myriagon with sides of length a is given by A =2500 a 2 cot ⁡ π10000 The result differs from the
1. A regular myriagon
65537-gon – In geometry, a 65537-gon is a polygon with 65537 sides. The sum of the angles of any non-self-intersecting 65537-gon is 11796300°. The regular 65537-gon is of interest for being a constructible polygon, that is, it can be constructed using a compass and this is because 65537 is a Fermat prime, being of the form 22n +1. Thus, the values cos ⁡ π65537
1. A regular 65537-gon
Megagon – A megagon or 1000000-gon is a polygon with 1 million sides. Even if drawn at the size of the Earth, a regular megagon would be difficult to distinguish from a circle. A regular megagon has an angle of 179. 99964°. The area of a regular megagon with sides of length a is given by A =250000 a 2 cot ⁡ π1000000, the perimeter of a regular megagon inscri
1. A regular megagon
Apeirogon – In geometry, an apeirogon is a generalized polygon with a countably infinite number of sides. It can be considered as the limit of a polygon as n approaches infinity. The interior of an apeirogon can be defined by a direction order of vertices. This article describes an apeirogon in its form as a tessellation or partition of a line. A regular apeir
1. Regular apeirogon
Star polygon – In geometry, a star polygon is a type of non-convex polygon. Only the regular polygons have been studied in any depth. The first usage is included in polygrams which includes polygons like the pentagram, star polygon names combine a numeral prefix, such as penta-, with the Greek suffix -gram. The prefix is normally a Greek cardinal, but synonyms us
1. {5/2}
Pentagram – A pentagram is the shape of a five-pointed star drawn with five straight strokes. The word pentagram comes from the Greek word πεντάγραμμον, from πέντε, five + γραμμή, the word pentacle is sometimes used synonymously with pentagram The word pentalpha is a learned modern revival of a post-classical Greek name of the shape. The pentagram is the simpl
1. Man inscribed in a pentagram, from Heinrich Cornelius Agrippa 's De occulta philosophia libri tres. The five signs at the pentagram's vertices are astrological.
2. A regular pentagram
3. The occultist and magician Eliphas Levi 's pentagram, which he considered to be a symbol of the microcosm, or human.
4. A goat's head inscribed in a downward-pointing pentagram, from La Clef de la Magie Noire by Stanislas de Guaita (1897).
Hexagram – A hexagram or sexagram is a six-pointed geometric star figure with the Schläfli symbol,2, or. It is the compound of two equilateral triangles, the intersection is a regular hexagon. It is used in historical, religious and cultural contexts, for example in Hanafism, Jewish identity, in mathematics, the root system for the simple Lie group G2 is in t
1. Diagram showing the two mystic syllables Om and Hrim
2. A regular hexagram
3. The Star of David in the oldest surviving complete copy of the Masoretic text, the Leningrad Codex, dated 1008.
4. Star of David on the Salt Lake Assembly Hall
Heptagram – A heptagram, septagram, or septogram is a seven-point star drawn with seven straight strokes. The name heptagram combines a numeral prefix, hepta-, with the Greek suffix -gram, the -gram suffix derives from γραμμῆς meaning a line. In general, a heptagram is any self-intersecting heptagon, there are two regular heptagrams, labeled as and, with the s
1. Former Georgian coat of arms, 1918–1921, 1991–2004
2. A regular heptagram
3. Flag of the Kingdom of Pentortoise
Octagram – In geometry, an octagram is an eight-angled star polygon. The name octagram combine a Greek numeral prefix, octa-, with the Greek suffix -gram, the -gram suffix derives from γραμμή meaning line. In general, an octagram is any self-intersecting octagon, the regular octagram is labeled by the Schläfli symbol, which means an 8-sided star, connected by
1. A regular octagram
Enneagram (geometry) – In geometry, an enneagram is a nine-pointed plane figure. It is sometimes called a nonagram, the name enneagram combines the numeral prefix, ennea-, with the Greek suffix -gram. The -gram suffix derives from γραμμῆς meaning a line, a regular enneagram is constructed using the same points as the regular enneagon but connected in fixed steps. It has
1. Enneagrams shown as sequential stellations
Decagram (geometry) – In geometry, a decagram is a 10-point star polygon. There is one regular decagram, containing the vertices of a regular decagon, the name decagram combine a numeral prefix, deca-, with the Greek suffix -gram. The -gram suffix derives from γραμμῆς meaning a line, for a regular decagram with unit edge lengths, the proportions of the crossing points o
1. A regular decagram
Hendecagram – In geometry, a hendecagram is a star polygon that has eleven vertices. The name hendecagram combines a Greek numeral prefix, hendeca-, with the Greek suffix -gram, the hendeca- prefix derives from Greek ἕνδεκα meaning eleven. The -gram suffix derives from γραμμῆς meaning a line and these same four forms can also be considered as stellations of a re
1. Fort Wood 's star-shaped walls became the base of the Statue of Liberty.
2. Four forms
Dodecagram – A dodecagram is a star polygon that has 12 vertices. A regular dodecagram has the vertex arrangement as a regular dodecagon. The name dodecagram combine a numeral prefix, dodeca-, with the Greek suffix -gram, the -gram suffix derives from γραμμῆς meaning a line. A regular dodecagram can be seen as a hexagon, t=. Other isogonal variations with equal
1. A regular dodecagram
Concave polygon – A simple polygon that is not convex is called concave, non-convex or reentrant. A concave polygon will always have at least one reflex interior angle—that is, some lines containing interior points of a concave polygon intersect its boundary at more than two points. Some diagonals of a concave polygon lie partly or wholly outside the polygon, some s
1. An example of a concave polygon.
Cyclic polygon – In geometry, the circumscribed circle or circumcircle of a polygon is a circle which passes through all the vertices of the polygon. The center of circle is called the circumcenter and its radius is called the circumradius. A polygon which has a circle is called a cyclic polygon. All regular simple polygons, all isosceles trapezoids, all triangles,
1. Circumscribed circle, C, and circumcenter, O, of a cyclic polygon, P
Regular polygon – In Euclidean geometry, a regular polygon is a polygon that is equiangular and equilateral. Regular polygons may be convex or star, in the limit, a sequence of regular polygons with an increasing number of sides becomes a circle, if the perimeter is fixed, or a regular apeirogon, if the edge length is fixed. These properties apply to all regular pol
1. The zig-zagging side edges of a n - antiprism represent a regular skew 2 n -gon, as shown in this 17-gonal antiprism.
2. Regular convex and star polygons with 3 to 12 vertices labelled with their Schläfli symbols
Polyform – In recreational mathematics, a polyform is a plane figure constructed by joining together identical basic polygons. The basic polygon is often a convex plane-filling polygon, such as a square or a triangle, more specific names have been given to polyforms resulting from specific basic polygons, as detailed in the table below. For example, a square
1. The 18 one-sided pentominoes: polyforms consisting of five squares.
Gnomon (figure) – Figurate numbers were a concern of Pythagorean mathematics, and Pythagoras is credited with the notion that these numbers are generated from a gnomon or basic unit. The gnomon is the piece needs to be added to a figurate number to transform it to the next bigger one. For example, the gnomon of the number is the odd number. For example, when transfo
1. A gnomon
Golygon – A golygon is any polygon with all right angles whose sides are consecutive integer lengths. Golygons were invented and named by Lee Sallows, and popularized by A. K, dewdney in a 1990 Scientific American column. Variations on the definition of golygons involve allowing edges to cross, using sequences of edge lengths other than the consecutive integ
1. An example of a simple 8-sided golygon
List of uniform tilings – This table shows the 11 convex uniform tilings of the Euclidean plane, and their dual tilings. There are three regular and eight semiregular tilings in the plane, the semiregular tilings form new tilings from their duals, each made from one type of irregular face. John Conway calls the uniform duals Archimedean tilings, in parallel to the Archimede
1. Periodic
2. Correspondence between families, as shown by labeled nodes of the Coxeter-Dynkin diagrams. The, [3 [3]] family symmetry is completely contained within, [6,3] symmetry cases. A doubling of the [4,4] symmetry produces another [4,4] symmetry.
Uniform tilings in hyperbolic plane – In hyperbolic geometry, a uniform hyperbolic tiling is an edge-to-edge filling of the hyperbolic plane which has regular polygons as faces and is vertex-transitive. It follows that all vertices are congruent, and the tiling has a degree of rotational and translational symmetry. Uniform tilings can be identified by their vertex configuration, a sequ
1. Periodic
Archimedean tiling – Euclidean plane tilings by convex regular polygons have been widely used since antiquity. The first systematic mathematical treatment was that of Kepler in his Harmonices Mundi and this means that, for every pair of flags, there is a symmetry operation mapping the first flag to the second. This is equivalent to the tiling being an edge-to-edge tili
1. Periodic
2. A regular tiling has one type of regular face.
Square tiling – In geometry, the square tiling, square tessellation or square grid is a regular tiling of the Euclidean plane. It has Schläfli symbol of, meaning it has 4 squares around every vertex, the internal angle of the square is 90 degrees so four squares at a point make a full 360 degrees. It is one of three regular tilings of the plane, the other two are
1. Periodic
2. Square tiling
Triangular tiling – In geometry, the triangular tiling or triangular tessellation is one of the three regular tilings of the Euclidean plane. Because the internal angle of the triangle is 60 degrees. The triangular tiling has Schläfli symbol of, Conway calls it a deltille, named from the triangular shape of the Greek letter delta. The triangular tiling can also be cal
1. Periodic
2. Triangular tiling
Hexagonal tiling – In geometry, the hexagonal tiling or hexagonal tessellation is a regular tiling of the Euclidean plane, in which three hexagons meet at each vertex. It has Schläfli symbol of or t, english mathematician Conway calls it a hextille. The internal angle of the hexagon is 120 degrees so three hexagons at a point make a full 360 degrees and it is one of
1. Chicken wire fencing
2. Graphene
3. Periodic
Truncated square tiling – In geometry, the truncated square tiling is a semiregular tiling by regular polygons of the Euclidean plane with one square and two octagons on each vertex. This is the only edge-to-edge tiling by regular polygons which contains an octagon. It has Schläfli symbol of t. Conway calls it a truncated quadrille, other names used for this pattern include
1. Periodic
2. Truncated square tiling
Snub square tiling – In geometry, the snub square tiling is a semiregular tiling of the Euclidean plane. There are three triangles and two squares on each vertex and its Schläfli symbol is s. Conway calls it a snub quadrille, constructed by a snub operation applied to a square tiling. There are 3 regular and 8 semiregular tilings in the plane, there are two distinct un
1. Periodic
2. Snub square tiling
Trihexagonal tiling – In geometry, the trihexagonal tiling is one of 11 uniform tilings of the Euclidean plane by regular polygons. It consists of triangles and regular hexagons, arranged so that each hexagon is surrounded by triangles. The name derives from the fact that it combines a hexagonal tiling. Two hexagons and two triangles alternate around each vertex, and it
1. Japanese basket showing the kagome pattern
2. Trihexagonal tiling
3. Periodic
Truncated hexagonal tiling – In geometry, the truncated hexagonal tiling is a semiregular tiling of the Euclidean plane. There are 2 dodecagons and one triangle on each vertex and it is given an extended Schläfli symbol of t. Conway calls it a truncated hextille, constructed as a truncation operation applied to a hexagonal tiling. There are 3 regular and 8 semiregular tilings
1. On painted porcelain, China
2. Truncated hexagonal tiling
3. Periodic
Rhombitrihexagonal tiling – In geometry, the rhombitrihexagonal tiling is a semiregular tiling of the Euclidean plane. There are one triangle, two squares, and one hexagon on each vertex and it has Schläfli symbol of rr. John Conway calls it a rhombihexadeltille and it can be considered a cantellated by Norman Johnsons terminology or an expanded hexagonal tiling by Alicia Boo
1. An ornamental version
2. Rhombitrihexagonal tiling
3. Church floor tiling, Sevilla, Spain
4. Periodic
Truncated trihexagonal tiling – In geometry, the truncated trihexagonal tiling is one of eight semiregular tilings of the Euclidean plane. There are one square, one hexagon, and one dodecagon on each vertex and it has Schläfli symbol of tr. There is only one uniform coloring of a trihexagonal tiling. A 2-uniform coloring has two colors of hexagons, 3-uniform colorings can have 3
1. Periodic
2. Truncated trihexagonal tiling
Snub hexagonal tiling – In geometry, the snub hexagonal tiling is a semiregular tiling of the Euclidean plane. There are four triangles and one hexagon on each vertex and it has Schläfli symbol of sr. The snub tetrahexagonal tiling is a hyperbolic tiling with Schläfli symbol sr. Conway calls it a snub hextille. There are 3 regular and 8 semiregular tilings in the plane an
1. Periodic
2. Snub trihexagonal tiling
Elongated triangular tiling – In geometry, the elongated triangular tiling is a semiregular tiling of the Euclidean plane. There are three triangles and two squares on each vertex and it is named as a triangular tiling elongated by rows of squares, and given Schläfli symbol, e. Conway calls it a isosnub quadrille. There are 3 regular and 8 semiregular tilings in the plane and t
1. Periodic
2. Elongated triangular tiling
Three-dimensional space – Three-dimensional space is a geometric setting in which three values are required to determine the position of an element. This is the meaning of the term dimension. In physics and mathematics, a sequence of n numbers can be understood as a location in n-dimensional space, when n =3, the set of all such locations is called three-dimensional Euclide
1. Three-dimensional Cartesian coordinate system with the x -axis pointing towards the observer. (See diagram description for correction.)
Regular polyhedron – A regular polyhedron is a polyhedron whose symmetry group acts transitively on its flags. A regular polyhedron is highly symmetrical, being all of edge-transitive, vertex-transitive and face-transitive, in classical contexts, many different equivalent definitions are used, a common one is that faces are congruent regular polygons which are assemble
1. Circogonia icosahedra, a species of Radiolaria.
1. {4,3} Defect 90°
3. Circogonia icosahedra, a species of radiolaria, shaped like a regular icosahedron.
4. Polyhedral dice are often used in role-playing games.
2. 4-sided die
1. Example of a non-sparking tool made of beryllium copper
2. Fluorite octahedron.
3. Two identically formed rubik's snakes can approximate an octahedron.
1. Cubic pyrite
2. Common dodecahedra
3. Pyritohedral
4. Ho-Mg-Zn quasicrystal
1. Convex regular icosahedron
1. This beach ball shows a hosohedron with six lune faces, if the white circles on the ends are removed.
2. The most familiar spherical polyhedron is the soccer ball, thought of as a spherical truncated icosahedron.
3. Periodic
1. Example hexagonal dihedron on a sphere
1. This beach ball shows a hosohedron with six lune faces, if the white circles on the ends are removed.
2. Example hexagonal hosohedron on a sphere
3. Periodic
2. Small stellated dodecahedron
3. Floor mosaic by Paolo Uccello, 1430
1. Transparent great stellated dodecahedron (Animation)
2. Great stellated dodecahedron