12 OAB is a sector of a circle, centre O, and radius 10 cm. AÔB = 72° and C is the point on the arc AB such that OC bisects AÔB. (a) Calculate the perimeter of sector OAB. (b) (i) Calculate the area of sector OAB. (ii) Calculate the total shaded area. (c) D is the point on the arc AB such that AÔD : DÔB = 1 : 2 . Gavin says that the shaded area on this diagram is the same as the shaded area calculated in part (b)(ii). Is he correct? Show your working.