# Exterior Angle of a Triangle

- Author:
- Anthony DiLaura

Explore the relationship between the sum of the two remote interior angles and the exterior angle of the third angle in a triangle by dragging sliders and making observations.

Drag the two sliders to transform the angle measures for angle A and B of the triangle. Compare the sum of these angles to the exterior angle at C in the triangle. Is this true for any triangle ABC?
1. What is the sum of the interior and exterior angles formed at point C in the triangle?
2. Create an acute triangle. What is the sum of angle A and B? What is the measure of the exterior angle at point C?
3. Create an obtuse triangle. What is the sum of angle A and B? What is the measure of the exterior angle at point C?
4. Make a conjecture about the relationship between the two remote interior angles of a triangle and the exterior angle of the third angle of a triangle?
Turn on the check box "show relationship" to check your conjecture.