In Fig.10.4, if ABC = 20 �, then AOC is equal to:

Given: ∠ABC = 20°

By theorem “The angle subtended by an arc at the center of a circle is twice the angle subtended by it at remaining part of the circle”, we have:

∠AOC = 2 × ∠ABC

= 2 × 20°

= 40°

∴ ∠AOC = 40°