Combination

[sami123]

A Diagonal Of a polygon is defined to be a line joining any two non-adjacent vertices.
a) Show that the number of diagonals in a 5-sided polygon
is (5 2) - 5
b) how many diagonals are there in 6-sided polygon?
c) show that the number of diagonals in an n-sided polygon is n(n-3) /2

 

[MarkFL]

c) You have \(n\) vertices from which to choose. To how many other vertices may we draw a diagonal? Will we count any diagonals twice?