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Module 15: Lesson 1
Interior & Exterior Angles
An interior angle of a polygon is one formed by the
sides of a polygon with a common vertex.
An exterior angle of a polygon is one formed by one
side of the polygon and the extension of an adjacent
side.
The Triangle Sum Theorem
The sum of the measures of the 3 interior angles of a triangle = 180°.
The Polygon Angle Sum Theorem
The sum of the measures of the interior angles of any polygon is
180°(n - 2) (where n is the number of sides of the polygon)
See example 1 on page 727.
A regular polygon is a polygon that has all sides of the
polygon with the same length and all interior angles with
the same measure.
2
1
3 4
The Exterior Angle Theorem
The measure of an exterior angle of a triangle is equal to the sum of the
measures of the 2 remote interior angles.
m4 = m1 + m2
2
1
3 4
1) Find the measures of the other 3 angles if m4 = 145, m1 = (5x - 2), m2 = 2x
2) Find the measures of the other 3 angles if m4 = (3x - 8), m1 = 90, m2 = x + 2
Homework pages 732-737 #’s 1-26 (all)