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Prove It Start by putting the line into its vector form. You need a parameter, say $\displaystyle \begin{align*} t \end{align*}$. So you can set $\displaystyle \begin{align*} x = t \end{align*}$, which means $\displaystyle \begin{align*} \frac{z - 1}{2} = t \implies z = 2t + 1 \end{align*}$.
So the line can be written as $\displaystyle \begin{align*} L = ( t, 1, 2t + 1 ) = t (1 , 0 , 2 ) + ( 0, 1, 1 ) \end{align*}$.
So the direction vector of the line is $\displaystyle \begin{align*} (1, 0, 2) \end{align*}$. What is the unit vector going in that direction? What is another unit vector that is parallel to this one?