Answer
$\|\mathbf{v}\|=\sqrt{30}$
Work Step by Step
$\mathbf{v}=2\mathbf{i}+5\mathbf{j}-\mathbf{k}$ and so
$\|\mathbf{v}\|=\sqrt{2^2+5^2+(-1)^2}=\sqrt{4+25+1}=\sqrt{30}$
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