Interior and Exterior Angles of Triangles
An immediate consequence of the Exterior Angle Theorem is the Exterior Angle Inequality Theorem.
Theorem. Exterior Angle Inequality Theorem
The measure of an exterior angle of a triangle is greater than that of each of its remote interior angles.
Prove this theorem as an exercise.
The following are the corollaries of the Exterior Angle Theorem:
Corollaries
| 1. | The acute angles of a right triangle are complementary. |
| 2. | There can be at most one right or obtuse angle in a triangle. |
