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.
Paliwanag
These are the basic circle theorems for angle measurements.