Title: Lesson 6-1
Author: mark_cameron
Last saved by: Glencoe Mathematics
Company: McGraw-Hill

Lesson 6-3

Example 1 Find the Sum on Interior Angle Measures
Find the sum of the measures of the interior angles of an octagon.

An octagon has 8 sides.

S = (n – 2)180			Write an equation.
S = (8 – 2)180			Replace n with 8.
S = (6)180 or 1,080		Simplify.

The sum of the measures of the interior angles of an octagon is 1,080°.

Example 2 Real-World Example

TESSELLATIONS A tessellation is a repeating pattern of shapes that completely covers a plane without overlapping. The tessellation below was constructed using squares, regular hexagons, and regular dodecagons. Find the measure of an interior angle of a regular dodecagon.

A dodecagon has 12 sides.

Step 1 Find the sum of the measures of the angles.

S = (n – 2)180			Write an equation.
S = (12 – 2)180		Replace n with 12.
S = (10)180 or 1,800		Simplify.

The sum of the measures of the interior angles of a regular dodecagon is 1,800°.

Step 2 Divide 1,800 by 12, the number of interior angles, to find the measure of one interior angle. So, the measure of one interior angle of a regular dodecagon is 1,800° ÷ 12 or 150°.