SOLUTION: How do you find the number of diagonals with just knowing the number of sides?

Question 557916: How do you find the number of diagonals with just knowing the number of sides?
Answer by scott8148(6628) (Show Source): You can put this solution on YOUR website!
the number of sides is the same as the number of corners (vertices)

diagonals are lines from corner-to-corner, that aren't sides

if there are N corners; you can draw lines from any corner, to N-1 other corners

but, the line from A to B is the same as the line from B to A
___ so the number of lines is {[N(N - 1)] / 2}

N of the lines are sides, so the number of diagonals is ___ {[N(N - 1)] / 2} - N ___ or ___ {[N(N - 3)] / 2}
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