# Exterior Angle Theorem

- Author:
- Rachel Slimovitch

1. Create a line segment. Label the endpoints B and D.
2. Create a point (C) on line segment BD.
3. Draw a triangle, with two of its vertices C and B. Call the third vertex A.
4. Measure all interior angles in the triangle. Also, measure the exterior angles (including ACD).
5. Move around vertex A on the triangle. As the triangle changes, notice the angle measurements changing.
6. Notice any relationships between the angles. Specifically, look at the exterior angle (ACD) and the interior angles.
7. Continue to move the triangle and make observations.

## Exterior Angle Theorem

What relationships have you noticed between the exterior angle, ACD, and the interior angles? Are there specific interior angles that follow a certain relationship rather than all the interior angles? State all conclusions you have found.