# Ch 5.1 Exterior Angle Theorem

- Author:
- David Greenstein

## Construction of the Exterior Angle Theorem

1. Construct a line through side AC of the triangle.
2. Construct a line through the vertex B that is parallel to side AC.
3. Measure the exterior angle at C and all three interior angles.
4. Observe the exterior angle measure and the sum of the remote interior angles. Move ABC and observe what happens to the angle measures.

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