Circle Theorems

Circle Theorems

1. Angles in the same segment are equal

2. Angle at the centre is twice the angle at the circumference

3. Angle in a semicircle is 90°

4. Opposite angles of a cyclic quadrilateral sum to 180°(are supplementary)

5. Angle between a tangent and radius is 90° at the point of contact

6. Tangents to a circle from an external point are equal in length

7. Alternate segment theorem

   • Angle between tangent and chord is equal