# How many sides does a regular polygon have if one exterior angle is 90?

The number of sides of regular polygon is $4$ and is a square.
Exterior angle (E) of a regular polygon is $E = \frac{360}{N}$. Where N is the number of sides of polygon . $\therefore 90 = \frac{360}{N} \mathmr{and} N = \frac{360}{90} = 4$
The number of sides of regular polygon is $4$ and is a square.[Ans]