The Inscribed Angle

Half the angle at the centre

An interactive lesson with 7 steps, about 6 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• The inscribed angle is half the central angle on the same arc.
• All inscribed angles on the same arc are equal.
• The proof uses isosceles triangles formed by radii.

Steps

1. Drag around the circle
2. Why it works
3. Use it
4. Make it 40°
5. Sliding into a tangent
6. Tangent and chord
7. The best seat