Hexagon
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In geometry, a hexagon is a six-sided polygon. The total of the internal angles of any simple (non-self-intersecting) hexagon is 720°.
Giant's Causeway closeup
The ideal crystalline structure of graphene is a hexagonal grid.
Assembled E-ELT mirror segments
A beehive honeycomb
Reflection symmetry
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In mathematics, reflection symmetry, line symmetry, mirror symmetry, or mirror-image symmetry is symmetry with respect to a reflection. That is, a figure which does not change upon undergoing a reflection has reflectional symmetry.
Many animals, such as this spider crab Maja crispata, are bilaterally symmetric.
Mirror symmetry is often used in architecture, as in the facade of Santa Maria Novella, Florence, 1470.