Question

if the number of diaganal in a regular polygon are 5 thrn find the no of sides of the polygon​

Answer 1

This regular polygon is a pentagon. It has 5 interior angles, each one is 108 degrees. So the sum of all of its interior angles is 5 x 108 degrees which is 540 degrees.

Answer 2

Four sides is two. So your polygon is coming up pretty quickly. If not you should skip to 8 sides or whatever you think would give you the next best piece of information. At five sides you will find there are five diagonals.