In figure, $BC$ is a diameter of the circle and $\angle BAO=60°$. Then, $\angle ADC$ is equal to

   

In the given figure, $\mathrm{AOC}$ is a diameter of a circle and $\mathrm{arc}\left(\mathrm{AXB}\right)=\frac{1}{2}\mathrm{arc}\left(\mathrm{BYC}\right)$. Find $\angle \mathrm{BOC}$.

In the given figure, $ABC$ is a triangle in which $\angle BAC=30°$. Show that $BC$ equals the radius of the circumcircle of $△ABC$, whose centre is $O$.