The group of symmetries of a regular one of these is isomorphic to the smallest non-Abelian group. Thales's theorem describes the angles of these polygons when inscribed in a 
The group of symmetries of a regular one of these is isomorphic to the smallest non-Abelian group. Thales's theorem describes the angles of these polygons when inscribed in a circle. Three of the platonic solids have these as faces. When a norm is applied to vectors that form the edges of one of these, the norms must satisfy this object's namesake inequality. A special case of Brahmagupta's formula named for Heron gives the area of these figures. Squares, hexagons, and these are the only regular polygons that can tile the plane. The law of cosines relates the lengths of their sides. For 10 points, name these simplest polygons, which come in scalene and isosceles varieties.
The group of symmetries of a regular one of these is isomorphic to the smallest non-Abelian group.