Question

If in a polygon the number of diagonals is $54$ then the number of sides of this polygon is?

Answer 1

number of diagonal in a 'n'polygon=54.

let it be a sided polygon.

diagonal can be made by combination of any two points expect adjecent points.

$n{c}_2-n=54$

$\frac{n(n-1)}{2}-n=54$

on solving

n=12.