Circle Properties Theorem 19

Theorem 19. The angle at the centre of a circle standing on a given arc is twice the angle at any point of the circle standing on the same arc.
Proof. There are several cases for the diagram. It will be suļ¬ƒcient for stu-[br]dents to examine one of these. The idea, in all cases, is to draw the line[br]through the centre and the point on the circumference, and use the Isosce-[br]les Triangle Theorem, and then the Protractor Axiom (to add or subtract[br]angles, as the case may be).
– Ronan Downes, BHNmath

Information: Circle Properties Theorem 19