A square with 3 points on each side used as vertices for triangulation (in addition to the vertices of the square) and 20 points inside the square is triangulated. What are all the possibilities for how many triangles are used in this triangulation?
Any hints or solutions will be appreciated.
I've tried looking at smaller cases, and I was looking at if it might be possible that there's only one possibility for the number of triangles. Then, how the triangles on the edges of the square can only be connected to one other point on the square, meaning it's connected to at least one point inside the square, but so far I haven't been able to get very far.