Circle theorems
Apply and prove circle theorems including tangent, chord and cyclic quadrilateral properties
What you'll learn
- 1
Imagine a pizza 🍕 with a dot right in the middle — that's the centre of the circle. A line from the centre to the edge is called a radius.
- 2
What is a line from the centre of a circle to the edge called?
- 3
Drag the points to make a triangle with one corner at the centre and two on the edge. Notice the two sides from the centre are equal — it's isosceles!
- 4
Let's prove: The angle at the centre is twice the angle at the edge (when they both see the same arc).
- 5
If the angle at the centre is 120°, what is the angle at the edge (on the same arc)?
- 6
Move point C around the circle — watch the angle at the edge stay half of the centre angle!
- 7
True or false: The angle at the centre is always bigger than the angle at the edge (on the same arc).
Practise Circle theorems with Whizlo
Free AI-tutored lessons, unlimited practice questions, and progress tracking for ages 14–16. Aligned to the UK National Curriculum.