Recall that the measure of each interior angle of a regular n -gon is ( n-2)180^(∘) n. To find the measure of an interior angle of a quadrilateral we have to substitute 4 for n in this expression.
( 4-2)180^(∘)/4= 90^(∘)
Because there are 4 sides, there are 4 angles. We can multiply this angle measurement by 4 to find the sum of the angles.
90^(∘) * 4 =360^(∘)
