The angle between the diagonals of a parallelogram $ABCD$, where $\overrightarrow {AB}=3\hat i-2\hat j+2\hat k$ and $\overrightarrow {BC}=-\hat i-2\hat k$ is?

Question

$\begin{array}{1 1} \large\frac{\pi}{6} \\ \end{array}$