Mathematics for IGCSE & O level - Circle Theorems (Section 2 - No. 41)

In a circle, which relationships can be used to find angle measures?

Angle at the center is twice angle at circumference.

Angles in the same segment are equal.

Opposite angles in a cyclic quadrilateral are supplementary.

The angle between the tangent and chord is equal to the angle in the alternate segment.

These are the basic circle theorems for angle measurements.