Example 9. In the dihedral angle $\alpha-\mathrm{a}-\beta$ of $120^{\circ}$, $\mathrm{A} \in \alpha, \mathrm{B} \in$ $\beta$, it is known that the distances from points $A$ and $B$ to the edge $a$ are 2 and 4, respectively, and $A B=$ 10. Find the angle formed by the line $\mathrm{AB}$ and the edge $\mathrm{a}$, and the angle formed by $\mathrm{AB}$ and the plane $\beta$.
(Answer: The angle between $\mathrm{AB}$ and edge a is $\arcsin \frac{\sqrt{7}}{5}, AB$ and $\beta$ is $\arcsin \frac{\sqrt{3}}{10}$.)
