Any n-sided convex polygon with more than 3 sides will have n(n-3)/2 diagonals.

For instance, let us look at a square. A square has 4 sides and 2 diagonals. Let us apply this formula with n = 4.

We get 4(4-3)/2 = 2 diagonals.

Here is a question on finding the number of diagonals.

If a n-sided convex polygon has 14 diagonals, how many sides does the polygon have?

Any n-sided convex polygon has n(n-3)/2 diagonals.

This polygon has 14 diagonals.

i.e., n(n-3)/2 = 14

Or n(n-3) = 28

Solving for n, we get n = 7.

So, the given polygon has 7 sides.

You can access sample practice questions on Geometry for your GMAT Prep by clicking here

Follow us on https://twitter.com/wizakoprep

WinningPrep says

i find your

GMAT Prepquestions very useful , thanks !!