The purpose of this page is to help you count a number of non-intersecting diagonals
in a convexpolygon.
I won't give you the formula right away. You are to come up with the right one by experimenting with the applet below.
Once you surmise the right result, try to prove it before looking into the explanation at the bottom of the page.
To draw diagonals just drag the mouse from one vertex to another. Remember that you are counting non-intersecting diagonals.