Circle theorems

What is circle theorems?

GCSE Maths circle theorems are a closed set of geometric rules about angles in a circle. The seven examinable rules: angle at the centre = 2× angle at the circumference; angle in a semicircle = 90°; angles in the same segment are equal; opposite angles in a cyclic quadrilateral sum to 180°; tangent meets radius at 90°; alternate segment theorem; tangents from an external point are equal.