HELP !!! A-level

Points A, B and C are on the circumference of a circle. Center O and radius r.

A trapezium OABC is formed such that AB is parallel to OC, and the angle og AOC (the angle of O) is delta, π/2 ≤ delta < π

a) shoe that the angle BOC (the angle of O) is π - delta

b) show that the area, T, of the trapezium can be expressed as

T = (1/2)r^2 sin(delta) - (1/2)r^2 sin2(delta)

c) show that when the area is maximun, the value of delta satisfies

Cos(delta) = 2cos2(delta)

Hence, determine the maximun area of the trapezium when r = 1