2 . In the rectangular prism $A B C D-A_{1} B_{1} C_{1} D_{1}$, $P$ and $Q$ are the midpoints of $A_{1} B_{1}$ and $B_{1} C_{1}$, respectively, $B_{:} B=B C=3, A B=4$. Then (1) the angle between $A_{2} C_{1}$ and $\mathrm{AB}_{1}$ is $\qquad$ , (2) the distance between $\mathrm{PQ}$ and $\mathrm{CD}$ is $\qquad$ .
$$
\text { 2. (1) } \arccos \frac{16}{25}
$$
(2) 3 .