Do not attempt to construct this with compass and straight edge . . . unless you just have extra time you want to waste. If constructing this were possible, then also possible would be the construction of a regular enneagon, and that has been proven impossible. To make this, I had to “cheat” by using rotations of 40°, using Geometer’s Sketchpad, which will let you play the construction-game by Euclid’s rules, or not, as you choose.