If the sum of the interior angles of a regular polygon is 1800°, how many diagonals does it have?
Show answer & explanation
Correct answer: C
Explanation
Sum of interior angles = 1800°
Sum = (n − 2) × 180
(n − 2) × 180 = 1800
n − 2 = 10
n = 12
Diagonals = n(n − 3)/2 = 12 × 9/2 = 54