Circle Theorems

Drag the points and watch each theorem hold.

Angle at the centre is twice the angle at the circumference

The angle at the centre of a circle is twice the angle at the circumference, when both are standing on the same arc.

Drag A, B or C. Put C on the short arc AB to see the reflex angle at the centre.

140 = 2 × 70

Exam tip: Write the reason as “angle at the centre is twice the angle at the circumference”.

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