The Central Angle Theorem states that the measure of
inscribed angle (∠APB)
is always half the measure of the central angle∠AOB.
As you adjust the points above, convince yourself that this is true.
This theorem only holds when P is in the
If P is in the
(that is, between A and B) the two angles have a different relationship.
In this case, the inscribed angle is the
of half the central angle. As a formula:
In other words, it is 180 minus what it would normally be.