Polygons and Diagonals[br]Number of diagonals in a polygon:[br]If n = number of vertex points, then D = number of diagonals = n(n-3)/2.[br]Slider n controls the number as well as the color. In the Advanced tab, [br]Red = n / 36, Green = 1 - n / 36, and Blue = 0, so the color changes from Green [br]to Red as the number of sides moves from 3 to 36.[br]reference: I modified sonom's idea from http://tube.geogebra.org/material/show/id/137056