Diagonal of a Polygon

A diagonal of a polygon is a line segment connecting two non-consecutive vertices of the polygon.

It should be noted that a line segment that connects two consecutive vertices of a polygon is a side of the polygon, not a diagonal. This means that triangles have no diagonals. The number of diagonals in an n-sided polygon can be calculated using the following formula. Number of Diagonals = n(n-3)/2