# Sum of the angles in a triangle

Before you check the box can you see how drawing a line through the top of the triangle parallel to the base will help to show that the sum of the three angles in a triangle is 180° ?

Directions:
1. Move the vertices of ∆ABC around.
2. Notice that the angles change when you move the vertices.
3. Pull the red slider to watch the animation.
4. What can you learn form this animation?

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