Question

The number of diagonals of a polygon is equal to the number of sides of the polygon . find the number of sides of the polygon

Answer 1

number of diagonal formula = $\frac{n(n-3)}{2}$, where n is number of sides.
here, $\frac{n(n-3)}{2}$ = n
So, $n^{2}-3n=2n$
$n^{2}=5n$
$\frac{ n^{2} }{n}=5$

So, we get n =5