Question

Find the value of a for which the vectors $3\hat{i}+3\hat{j}+9\hat{k}$ and $\hat{i}+a\hat{j}+3\hat{k}$ are parallel.

Answer 1

Two vectors are parallel, if one vector is scalar multiple of other. Thus

$\frac{3}{1}=\frac{3}{a}=\frac{9}{3}$

$\frac{3}{a}=3$

$a=1$