Find the number of diagonals of a polygon of 20 sides

Find the number of diagonals of a polygon of 10 sides.

The number of diagonals of a polygon of 15 sides is:

Find the numbers of diagonals in the polygon of n sides.

The number of diagonals of a polygon of 20 sides si (A) 25 (B) 150 (C) 170 (D) 210

A regular polygon has 20 sides. Find the number of diagonals of the polygon.

The number of diagonals of a convex polygon of sides n is equal to (n(n-3))/(2) . Find the number of diagonals is hexagon.