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Geometry & MeasuresExam Tips

Common Mistakes

Part of Circle Theorems — GCSE Mathematics

This exam tips covers Common Mistakes within Circle Theorems for GCSE Mathematics. Revise Circle Theorems in Geometry & Measures for GCSE Mathematics with 18 exam-style questions and 5 flashcards. This topic shows up very often in GCSE exams, so students should be able to explain it clearly, not just recognise the term. It is section 5 of 5 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.

Topic position

Section 5 of 5

Practice

18 questions

Recall

5 flashcards

Common Mistakes

X Angle at circumference = 2× angle at centre Angle at CENTRE = 2× angle at circumference Don't reverse the relationship!
X Adjacent angles in cyclic quad = 180° OPPOSITE angles in cyclic quad = 180° Must be opposite, not adjacent

Keep building this topic

Read this section alongside the surrounding pages in Circle Theorems. That gives you the full topic sequence instead of a single isolated revision point.

Worked Example: Centre and CircumferenceThe Geometry of PizzaThe Eight Circle Theorems

Practice Questions for Circle Theorems

AB is a diameter of a circle. Point C lies on the circle. What is the size of angle ACB?

  • A. 45°
  • B. 60°
  • C. 90°
  • D. 180°
1 markfoundation

State the circle theorem used to find angle x in the diagram, and explain why it applies in this situation.

2 marksstandard

Quick Recall Flashcards

Angle in Semicircle
Any angle inscribed in a semicircle (with diameter as base) is always 90°. Always!
Cyclic Quadrilateral
If all 4 vertices lie on a circle, opposite angles sum to 180°. Also works in reverse: if opposite angles sum to 180°, then it's cyclic!

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Worked Example: Centre and Circumference

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Circle Theorems