Octagon

The octagon, or oc, is a polygon with 8 sides. A regular octagon has equal sides and equal angles.

The combining prefix is o-, as in odip.

The only non-compound stellation of the octagon is the octagram. The only other polygons with a single non-compound stellation are the pentagon, the decagon, and the dodecagon.

It can also be constructed as a uniform truncation of the square.

Naming
The name octagon is derived from the Ancient Greek (8) and  (angle), referring to the number of vertices.

Other names include:


 * Oc, Bowers style acronym, short for "octagon".

Vertex coordinates
Coordinates for an octagon of unit edge length, centered at the origin, are all permutations of
 * $$\left(±\frac{1+\sqrt2}{2},\,±\frac12\right).$$

Representations
A regular octagon can be represented by the following Coxeter diagrams:


 * x8o (full symmetry)
 * x4x (BC2 symmetry, generally a ditetragon)
 * ko4ok&#zx (BC2, generally a tetrambus)
 * xw wx&#zx (digonal symmetry)
 * okK Kko#&zx (digonal symmetry, K=qk)
 * xwwx&#xt (axial edge-first)
 * okKko&#xt (axial vertex-first)

Variations
Two main variants of the octagon have square symmetry: the ditetragon, with two alternating side lengths and equal angles, and the dual tetrambus, with two alternating angles and equal edges. Other less regular variations with rectangular, mirror, or no symmetry also exist.

Stellations

 * 1st stellation: Stellated octagon (compound of two squares)
 * 2nd stellation: Octagram