Enneagram

The enneagram, or eng, is a non-convex polygon with 9 sides. Its created by taking the first stellation of an enneagon. A regular enneagram has equal sides and equal angles.

It is one of two regular 9-sided star polygons, the other being the great enneagram. The name "enneagram" is often used to describe either of these two shapes.

Vertex coordinates
Coordinates for a regular enneagram of edge length 2sin(2π/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)).