Question

Two angles of a

polygon are 90° and each
of the other is 120°
find the no. of sides.
​

Answer 1

`5\ sides`

Explanation:

we know that

The formula to calculate the sum of the interior angles in a polygon is equal to

`S=(n-2)180^o` ----> equation A

where

n is the number of sides of the polygon

In this problem we have that the sum is equal to

`S=2(90^o)+(n-2)120^o` ---> equation B

Equate equation A and equation B

`(n-2)180^o=2(90^o)+(n-2)120^o`

solve for n

Applying distributive property both sides

`180n-360=180+120n-240`

Group terms

`180n-120n=180-240+360`

Combine like terms

`60n=300`

Divide by 60 both sides

`n=5\ sides`