# The side of a parallelogram are $2 \hat i +4 \hat j -5 \hat k$ and $\hat i +2 \hat j +3 \hat k$, then the unit vector parallel to one of the diagonals is :
$\begin{array}{1 1} \frac{1}{7} (3 \hat i +6 \hat j -2 \hat k) \\\frac{1}{7} (-3 \hat i +6 \hat j -2 \hat k) \\ \frac{1}{7} (-3 \hat i +6 \hat j +2 \hat k) \\ \frac{1}{7} (3 \hat i +6 \hat j +2 \hat k) \end{array}$