In Fig. 10.8, BC is a diameter of the circle and BAO = 60º. Then ADC is equal to:
Fig. 10.8
(A) 30º
(B) 45º
(C) 60º
(D) 120º
(C)
Solution:
In AOB, AO = OB (Radius)
ABO = BAO [Angle opposite to equal sides are equal]
ABO = 60° [ BAO = 60° Given]
In AOB,
ABO + OAB =AOC (exterior angle is equal to sum of interior opposite angles)
60° + 60° = 120° =AOC
(Angle subtended at the centre by an arc is twice the angle subtended by it at any part of the circle)
ADC = 60°
Therefore option (C) is correct.