Question

In the following figure, $m($arc $APC)={60}^o$, find $\angle ABC$.

Answer 1

In a circle angle subtended by any chord on opposite sides are supplementary.

So $m\left(arcAPC\right)+m\left(arcABC\right)={180}^o$

So $m\left(arcABC\right)={180}^o-{60}^o={120}^o$