GCSE Maths Practice: circle-theorems

Question 5 of 10

This question focuses on the semicircle theorem: the angle at the circumference opposite the diameter is always 90°.

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\( \begin{array}{l}\text{What is the size of the angle formed at the circumference in a semicircle?}\end{array} \)

Choose one option:

Angle opposite diameter in semicircle = 90°.

In a semicircle, the angle formed at the circumference by the diameter as the base of a triangle is always a right angle (90°). This is a key property in circle geometry, often used in proofs, constructions, and calculations. Understanding this theorem helps students solve problems involving triangles inscribed in circles, tangents, and cyclic quadrilaterals. It reinforces reasoning about perpendicularity and angles formed by arcs. Applying this knowledge ensures accurate identification of right angles in diagrams and geometric proofs in GCSE questions.