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QUESTION

Find the angle between the vectors $\textbf{c}=\textbf
{i}+3\textbf{j}$ and
$\textbf{d}=3\textbf{i}-\textbf{j}+2\textbf{k}$.

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ANSWER

$\textbf{c.d}=(1,3,0).(3,-1,2)=3-3+0=0$ i.e.
$\cos\theta=0,\theta=\frac{\pi}{2}$




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