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 20-gon we have to substitute 20 for n in this expression.
( 20-2)180^(∘)/20= 162^(∘)
Because there are 20 sides, there are 20 angles. We can multiply this angle measurement by 20 to find the sum of the angles.
162^(∘) * 20 =3240^(∘)
