Question

Does anyone know of a theorem or equation that will determine how many diagonals a polygon has, without having to do a drawing to see how many there are?

Answer 1

`nxx(n-3)/2`

where, n is the number of sides

Explanation:

For example ...

triangle: `3xx(3-3)/2=0` diagonals

pentagon: `5xx(5-3)/2=5` diagonals

Source: http://www.dummies.com/how-to/content/how-to-find-the-number-of-diagonals-in-a-polygon.html

hope that helped