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For which real numbers $x$ is $\begin{bmatrix} x \\\ 2x \\\ 3x \end{bmatrix}$ a unit vector?

Select ALL that apply.

$\pm\dfrac{1}{14}$

$\pm\dfrac{1}{7}$

$\pm\dfrac{1}{2}$

$\pm\dfrac{1}{\sqrt{14}}$

$\pm\dfrac{1}{\sqrt{7}}$