Activity 4.2.8: Triangle Exterior Angle Sum Theorem

Consider the triangle below. The sides of the triangle have been extended to produce an exterior angle at each vertex.

Use the angle tool to measure angles α, β, and γ.

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What is the sum of the three angles?
Will this always be the case?
How can you test your conjecture?

Kelly Shattuck, July 1, 2008, Created with GeoGebra