What is it
Circle theorems are a set of angle and length facts specific to circles — such as the angle in a semicircle being 90°, or the angle at the centre being twice the angle at the circumference — used to solve geometric problems involving circles.
Why it matters
Circle theorems are one of the most heavily weighted topics at GCSE Higher tier, and questions typically require chaining two or three theorems together — genuine multi-step geometric reasoning.
Exam tip
Sketch and label the diagram clearly before starting, marking every angle you're given — spotting which theorem applies is far easier once the diagram is clearly annotated.
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