Question:
In figure, if $\angle A B C=20^{\circ}$, then $\angle A O C$ is equal to
(a) $20^{\circ}$
(b) $40^{\circ}$
(c) $60^{\circ}$
(d) $10^{\circ}$
Thinking Process
Use the theorem, that in a circale the angle subtended by an arc at the centre is twice the angle subtended by it at the remaining part of the circle and
further simplify it.
Solution:
(b) Given, ∠ABC = 20°
We know that, angle subtended at the centre by an arc is twice the angle subtended by it at the remaining part of circle.
∠AOC = 2∠ABC = 2 x 20° = 40°