coordinate

??????????
what?? is this a question???
wat do mean by0 no of permutation in a polygon?

sorry there is some mistake in question i edited it
look it now

ok
the polygon has n sides
so for making a diagonal we have to have two points

therefore no of such cases is selecting 2 points out of n points i polygon
=nC2
but out of these some cases are there in which we have selected two adjacent points .....no of such adjacent points =n

therefore total no of diagonals= nC2 - n

ans= n(n-3)2