1. Circle Theorems

2. Angle in a Semicircle
There is always a 90º angle opposite the diameter.

3. Angle at the Centre is Twice the Angle
at the Circumference X Y

4. Opposite Angles in a Cyclic Quadrilateral
add up to 180º X Y

5. Angles in the Same Segment are the SameX

6. Radius and Tangent meet at 90º

7. A B C
AC=BC
Any two tangents from the same point are the same length. The angle between the tangent and the radius drawn to meet it is 90º.

8. Alternate Segment TheoremX Y
There are two pairs of equal angles. One made at the tangent line is equal to the angle in the triangle on the opposite side.

9. Questions
Find angle a and b
Find angle a and b
Find angle c and d
Find angle b