We will cover the n-gon with triangles whose only angles make up some
or all of the interior angles of the n-gon. We can do this by picking
one specific corner and drawing lines from the corner to each of the
There will be n-3 such lines to draw, and each will separate off 1
triangle except the last will separate 2. Thus (n-2) triangles cover
the n-gon, so the n-gon will have a sum of interior angles equal to
180(n-2) degrees. For a regular n-gon we have n corners, all with the
same angle, so that angle is...