AB is a diameter of a circle with centre O. If C is any point on the circle such that ∠BAC = 42°, then find the measure of ∠BOC.

60° 63° 42° 84°

84°

We know that ∠BAC is the angle of circumference. The angle made on the center by a chord is double the angle made on the circumference by the same chord. ∠BOC = 2∠BAC = 2 × 42° = 84°