In the given figure O is the centre, then find ∠ACB ?
OA = OB (radius) Then ∠OAB = ∠OBA = 30° {Angle subtended by the radius to the centre is} ∠AOB = 180 - (∠OAB+∠OBA) = 180 - 30 - 30 = 120° Major ∠AOB = 360 - 120 = 240° Then ∠ACB = 1/2 × 240 = 120° {Angle subtended in the arc is half of that subtended at the centre.}