Central Angle and Circumscribed Angle Formed by Tangent Line

Drag points A, B, and C and make observations about the relationship between Angles A and C.
What do you notice about the relationship between ∠α and∠β?[br]What is the word for that kind of relationship?
– Jessica Cummings, Katie Finley

Information: Central Angle and Circumscribed Angle Formed by Tangent Line