Solution to #4-2

Paper 1 Difficulty:Medium

Let $latex \vec{u}=\begin{pmatrix} 3\\ k\\ -2 \end{pmatrix}$, and $latex \vec{v}=\begin{pmatrix} 5\\ -2\\ 7 \end{pmatrix}$, for $latex k>0$. The angle between $latex \vec{u}$ and $latex \vec{v}$ is $latex \frac{\pi }{2}$ radians.

Find the value of k.

[Maximum mark:5]


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