Aspire Faculty ID #16201 · Topic: NIMCET 2011 · Just now
NIMCET 2011

$ \vec{v} = 2\hat{i} + \hat{j} - \hat{k},\quad \vec{w} = \hat{i} + 3\hat{k} $ If $ \vec{u} $ is a unit vector, maximum value of $ [\vec{u}\ \vec{v}\ \vec{w}] $ is:

Solution

$$ \vec{v} \times \vec{w} = \begin{vmatrix} \hat{i} & \hat{j} & \hat{k} \\ 2 & 1 & -1 \\ 1 & 0 & 3 \end{vmatrix} $$ $$ = 3\hat{i} - 7\hat{j} - 1\hat{k} $$ $$ |\vec{v} \times \vec{w}| = \sqrt{3^{2} + (-7)^{2} + (-1)^{2}} = \sqrt{9 + 49 + 1} = \sqrt{59} $$ $$ \boxed{\sqrt{59}} $$

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