Math 9: Central and Inscribed Angles
A Central Angle is one formed by two radii of a circle (shown in blue). Inscribed angles are formed by two chords (green). What do you notice about the central angle and the inscribed angle? What happens if you change one of the angles (by moving a point along the circle)?
The rule: The measure of the central angle is equal to twice the measure of the inscribed angle subtended by the same arc.