1. ANGLES OF A TRIANGLE Section 4.2

2. Angles of a Triangle Interior angles  Original three angles of a triangle Exterior angles  Angles that are adjacent to interior angles

3. Theorem 4.2 Triangle Sum Theorem  The sum of the measures of the interior angles of a triangle are 180° m<1= m<2= m<3=

4. Theorem 4.3 Third Angles Theorem  If two angles of one triangle are congruent to two angles of a second triangle, then the third angles are also congruent Theorem 4.4 The acute angles of a right triangle are complementary.

5. More Theorems Theorem 4.5 Exterior Angle Theorem: The measure of an exterior angle of a triangle is equal to the sum of the measures of the two remote interior angles. m<1= m<B + m<A

6. Thms. Cont. Theorem 4.6: Exterior Angle Inequality  The measure of an exterior angle of a triangle is greater than the measure of either of the two remote interior angles. m m<B or m<A

7. Finding Angle Measures