OR (b) Find the shortest distance between the lines $L_1$ & $L_2$ given below : $L_1 :$ The line passing through $(2, -1, 1)$ and parallel to $\frac{x}{1} = \frac{y}{1} = \frac{z}{3}$ $L_2 : \vec{r} = \hat{i} + $2\mu + 1$\hat{j} - (\mu + 2)\hat{k}$.