Question

A line segment can be drawn from each vertex of a polygon to every other vertex, forming the sides and diagonals of the polygon. A square, for example, has 4 sides and 2 diagonals. Using combinations, write an expression that would give you the total number of sides and diagonals for a polygon with n sides.

Answer 1

n vertices by (n-3) (triangle division from a vertex) is 2n

So half of that in order not to double count is n(n-3)/2