Question

a polygon has 90 diagonals. how many sides does it have?​

Answer 1

Answer:

n(n-3)/2=no of diagonals

n(n-3)/2=90

n^2 - 3n=180

n^2 - 3n-180=0

$- b + or - \sqrt{b} {}^{2} - 4ac \div 2a$

3+- 27/2

=3+27/2=30/2=15

=3-27/2=-24/2=-12

Therefore it has 15 sides