4. A circle with center at point $O$ touches side $B C$ of triangle $A B C$ at point $C$ and touches median $A D$ of triangle $A B C$ at point $A$. $O B$ is the bisector of angle $A O D$. Find the angles of triangle $A B C$.
4. $\frac{\pi}{2}, \arccos \frac{\sqrt{17}-1}{4}, \arcsin \frac{\sqrt{17}-1}{4}$.