Polygon angles
Answers are for parents and teachers.
1
Find the interior angle sum of a polygon with 12 sides.
(12 − 2) × 180° = 1800°.
2
Four angles of a pentagon are 120°, 100°, 90° and 130°. Find the fifth.
540° − 440° = 100°.
3
Find each interior and exterior angle of a regular polygon with 18 sides.
Exterior 20°; interior 160°.
4
Each interior angle of a regular polygon is 144°. How many sides?
Exterior 36°; 360 ÷ 36 = 10.
5
A polygon has 20 diagonals. How many sides?
n(n − 3) = 40; 8 × 5 = 40, so n = 8.