Angles of Triangles

Angles Interior angles Exterior angles

4.1: Triangle Sum Theorem

Examples triangle sum theorem

4.2 Exterior Angle Theorem Remote Interior Angles 2 Exterior Angle 3 1

Examples Exterior angle theorem

3 4. 4

Ex 5: Find the measure of each numbered angle in the figure below. 65 82 46 1 5 142 2 4 3

Example 6 Find x and the x 2x + 21

Example 7 Find x and the 2x x X - 20

Example 8 Find x and the 80 3x - 22 x

Example 9: Find the 80 3x +6 x

Third Angle Sum Theorem If two angles of a triangle are congruent to two angles of a second triangle, then the third angles of the triangles are congruent.

Corollaries 4.1 : The acute angles of a right triangle are complementary. 4.2 : There can be at most one right or obtuse angle in a triangle.

10 11.