Angle at the centre of a circle is twice the angle at the circumference
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:
- 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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