Help solving the explicit solution for the following recursive expression:

[Gotcha]

Hello,

here i need to find the explicit solution for the following recursive expression: (Thanks for any suggestions)

A diagonal in a polygon it is a line of a vertex to another vertex that is not adjacent. For example, a triangle does not have diagonals. Find the number of diagonals in a polygon of n sides where n >= 3.

[Narue]

Stop posting your homework for other people to do.