In a certain regular polygon, the measure of each interior angle is 12 times the measure of each exterior angle. Find the number of sides in this regular polygon.
The formula for the value of each interior angle of a regular polygon is (n - 2)(180o) / n
Each interior angle = 180o - the exterior angle and each exterior anlge = 180o - the interior angle.
"each interor angle is 12 times the measuure of each interior angle"
---> (n - 2)(180o) / n = 12 · ( 180o - (n - 2)(180o) / n )
---> (n - 2)(180o) / n = 2160o - 12 · (n - 2)(180o) / n ) [distribute the 12]
---> (n - 2)(180o) / n + 12 · (n - 2)(180o) / n ) = 2160o [add 12 · (n - 2)(180o) / n ) to both side]
---> 13 · (n - 2)(180o) / n ) = 2160o [simplify]
---> 13 · (n - 2)(180o) = 2160o · n [multiply both sides by n]
---> 2340 · n - 4680o = 2160o · n [multiply out the left side]
---> 180o · n = 4680o
---> n = 26 sides