1.

 In the diagram, A, B, C and D are points on the circumference of a circle with

 centre O. AB is a diameter of the circle and . Find

(a) , (b) .

2.

 In the diagram, the points A, B, C and D lie on the circumference of a circle with

 centre O. TB is a tangent to the circle and BD is a diameter of the circle. Given

 that and . Find