During the February 26th MoMath Masters Tournament, @MoMath1 tweeted, “No googling – how many sides on an enneagon?” We thought, “Hey! We know enneagons!” If you don’t, maybe this scenario from a problem we first used in 1998 will give you some hints (as well as some ideas for something you could do with one).
Extending the Enneagon
Extend the sides AB and ED of the regular enneagon ABCDEFGHI until they intersect.
I noticed that the enneagon has 9 vertices ABCDEFGHI. I noticed that when you extend two sides of the shape, they will intersect. I wonder how many sides an enneagon has?