(a) Make d the subject of the formula \(S = \frac{n}{2}[2a + (n - 1) d]\).

(b) (i) 

In the diagram, O is the centre of the circle, A, B and P are points on the circumference. Prove that < AOB = 2 < APB.

(ii) 

Find the angles x, v and z in the diagram.