Enneagon

The enneagon or en, sometimes referred to as a nonagon, is a non-convex polygon with 9 sides. A regular enneagon has equal sides and equal angles.

It has two stellations, these being the enneagram and the great enneagram.

Vertex coordinates
Coordinates for an enneagon of edge length 2sin(π/9), centered at the origin, are:


 * (1, 0),
 * (cos(2π/9), ±sin(2π/9)),
 * (cos(4π/9), ±sin(4π/9)),
 * (–1/2, ±$\sqrt{3}$/2),
 * (cos(8π/9), ±sin(8π/9)).