7 Throughout this question leave all answers as exact expressions in terms of it and 2n square roots for example 2 n 3 or etc In the diagram below the circle centred at O has radius 3cm The curved line AOC is part of a circle also of radius 3cm centred at D OD is perpendicular to AC a Calculate the length AB DIAGRAM 1 b Calculate the area of triangle AOC A B D c Calculate the area of sector OADC in diagram 1 indicated for refere 2 below DIAGRAM 2 B A d Calculate the shaded area indicated in diagram 1 D 1