Angles Inscribed in a Semicircle - Law of Thales
Angle APB intercepts a semicircle. 
Drag points A to change the orientation of the semicircle.
Drag point P to change the angle. 
1.
Angle APB intercepts a semicircle. Drag points A to change the orientation of the semicircle. Drag point P to change the angle. Does the measure of the angle APB ever change? What might be generalized about an angle that intercepts a semicircle?