Answer
$\sqrt{116}$
Work Step by Step
Therefore,
$\begin{align}
& 2\mathbf{u}=\left[ 2\times \left( 2 \right) \right]\mathbf{i}+\left[ 2\times \left( -5 \right) \right]\mathbf{j} \\
& =4\mathbf{i}-10\mathbf{j}
\end{align}$
And
$\begin{align}
& \left\| 2\mathbf{u} \right\|=\sqrt{{{4}^{2}}+{{10}^{2}}} \\
& =\sqrt{16+100} \\
& =\sqrt{116}
\end{align}$
