Circle theorems (advanced)

What you'll learn

1. 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 crust is called the radius.

2. 2

   If the radius of a circle is 5 cm, how long is the diameter?

3. 3

   Tap on the circle to mark the centre, then draw a radius and a diameter by tapping the correct points.

4. 4

   A chord is a straight line joining two points on the edge of a circle — like a slice of pizza crust. Let's find the angle at the centre.

5. 5

   In a circle, if the angle at the centre is 80°, what is the angle at the edge (on the same chord)?

6. 6

   Drag the points on this circle to make a chord and see the angle at the centre change. What happens to the edge angle?

7. 7

   A triangle drawn inside a circle with one side as the diameter always has a right angle opposite the diameter. What is that right angle called?