Enneagon

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

Vertex coordinates
Coordinates for a heptagon 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)).