4.3Exterior Angle Theorem
Quick Answer
Exterior Angle Theorem: an exterior angle of a triangle equals the sum of the two non-adjacent (remote) interior angles. Exterior angle = remote interior angle 1 + remote interior angle 2.
Essential Question
How does the Exterior Angle Theorem relate an exterior angle to the interior angles of a triangle?
Learning Goals
- 1Identify exterior angles and remote interior angles.
- 2State the Exterior Angle Theorem.
- 3Apply the theorem to find missing angle measures.
- 4Prove the Exterior Angle Theorem using the Angle Sum Theorem.
Key Vocabulary
Exterior angle
An angle formed by one side of a polygon and the extension of an adjacent side.
Remote interior angles
The two interior angles of a triangle that are not adjacent to a given exterior angle.
Exterior Angle Theorem
An exterior angle of a triangle equals the sum of its two remote interior angles.
Full lesson content coming soon
Worked examples, guided practice problems, a workbook, quiz, and downloadable PDF resources will be added to this lesson in Phase 2. The learning goals and vocabulary above reflect the complete lesson scope.