The sum of the measures of the interior angles of an n-gon is
(n - 2)180
In a 9-gon, there are 9 sides, so n = 9.
The sum of the measures of the interior angles of a 9-gon is
(n - 2)180 =
= (9 - 2)(180)
= 7(180)
= 1260
A regular polygon has congruent interior angles. A 9-gon has 9 congruent interior angles. The measure of each interior angle is the sum of the measures of the interior angles divided by the number of angles.
