Updated on June 13, 2014

#### Objectives

- Find the central angle measure of a regular polygon
- Relate the sum of the interior angles of a triangle to the sum of the interior angles of a regular polygon
- Apply geometric representations of the expressions (
*n*– 2)180 and 180*n*– 360 to determine the measure of the interior angles of a regular polygon

#### Vocabulary

- Central angle
- Base angle
- Interior angle
- Isosceles triangle
- Regular polygon

#### About the Lesson

This lesson involves changing the number of sides of a regular polygon. As a result students will observe the consequences of this manipulation on the central angle; infer the relationship between the central angle and the number of sides of a regular polygon; infer the relationship between the base angles of the isosceles triangles and the measure of an interior angle; deduce the geometric and algebraic equivalence of the expressions (*n* – 2)180 and 180*n* – 360, which can be used to find the interior angle sum of all regular and irregular convex polygons.