# Angle at the centre of a circle is twice the angle at the circumference

Martin McBride

2020-08-16

For any chord, we can draw two lines to form an angle at the centre of the circle, angle **a**.

We can also draw two lines to form an angle at the circumference, **b**.

The angle at the centre of a circle is twice the angle at the circumference.

This theorem is covered in this video on circle theorems:

## See also

- Tangent and radius of a circle meet at 90°
- Two radii form an isosceles triangle
- Perpendicular bisector of a chord
- Angle in a semicircle is 90 degrees

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