If the vectors $\overrightarrow{\mathrm{a}}=\hat{\mathrm{i}}-\hat{\mathrm{j}}+2 \hat{\mathrm{k}},…

If the vectors $\overrightarrow{\mathrm{a}}=\hat{\mathrm{i}}-\hat{\mathrm{j}}+2 \hat{\mathrm{k}}, \overrightarrow{\mathrm{b}}=2 \hat{\mathrm{i}}+4 \hat{\mathrm{j}}+\hat{\mathrm{k}}$ and $\overrightarrow{\mathrm{c}}=\lambda \hat{\mathrm{i}}+\hat{\mathrm{j}}+\mu \hat{\mathrm{k}}$ are mutually orthogonal, then $(\lambda, \mu)=$
  1. $(2,-3)$
  2. $(-2,3)$
  3. $(3,-2)$
  4. $(-3,2)$

Solution

$ \begin{aligned} & \vec{a} \cdot \vec{b}=0, \quad \vec{b} \cdot \vec{c}=0, \quad \vec{c} \cdot \vec{a}=0 \\ & \Rightarrow 2 \lambda+4+\mu=0 \quad \lambda-1+2 \mu=0 \\ & \end{aligned} $ Solving we get: $\lambda=-3, \mu=2$

Asked in: JEE Main 2010

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