Fissal enneagram

The fissal enneagram, or fen, is a polygon compound composed of 3 triangles. As such it has 9 edges and 9 vertices.

Vertex coordinates
Coordinates for the vertices of a fissal enneagram of edge length 1 centered at the origin are given by:
 * ($\sqrt{3}$/3, 0),
 * ($\sqrt{3}$cos(2π/9)/3, ±$\sqrt{3}$sin(2π/9)/3),
 * ($\sqrt{3}$cos(4π/9)/3, ±$\sqrt{3}$sin(4π/9)/3),
 * (–$\sqrt{3}$/6, ±1/2),
 * ($\sqrt{3}$cos(8π/9)/3, ±$\sqrt{3}$sin(8π/9)/3).