Given : $$angle$$ ACB = $$15^circ$$ To find : $$angle$$ OAB = $$x=?$$ Solution : Angle subtended by an arc at the centre is double the angle subtended by the same arc at any other point on the circle. => $$angle$$ AOB = $$2 imes15^circ=30^circ$$ -------------(i) Also, in $$ riangle$$ AOB, OA = OB = radius of circle, => $$angle$$ OAB = $$angle$$ OBA = $$x$$     [Angles opposite to equal sides] Thus, in $$ riangle$$ AOB => $$angle x+$$ $$angle x+$$ $$angle$$ AOB = $$180^circ$$ => $$2angle x=180^circ-30^circ$$    [Using equation (i)] => $$angle x=frac{150^circ}{2}=75^circ$$  => Ans - (C)