JEE Main & Advanced Mathematics Vector Algebra Question Bank Application of vectors in three dimensional geometry

  • question_answer
    Angle between the line \[\mathbf{r}=(\mathbf{i}+2\mathbf{j}-\mathbf{k})+\lambda (\mathbf{i}-\mathbf{j}+\mathbf{k})\] and the normal to the plane \[\mathbf{r}\,.\,(2\mathbf{i}-\mathbf{j}+\mathbf{k})=4\] is [MP PET 1997]

    A)            \[{{\sin }^{-1}}\,\left( \frac{2\sqrt{2}}{3} \right)\]

    B)            \[{{\cos }^{-1}}\,\left( \frac{2\sqrt{2}}{3} \right)\]

    C)            \[{{\tan }^{-1}}\,\left( \frac{2\sqrt{2}}{3} \right)\]

    D)            \[{{\cot }^{-1}}\,\left( \frac{2\sqrt{2}}{3} \right)\]

    Correct Answer: A

    Solution :

               The plane is \[2x-y+z=4\] and the line is \[\frac{x-1}{1}=\frac{y-2}{-1}=\frac{z+1}{1}\]                    \[\therefore \,\,\,\sin \theta =\frac{2+1+1}{\sqrt{6}\sqrt{3}}=\frac{4}{\sqrt{18}}=\frac{2\sqrt{2}}{3}\Rightarrow \theta ={{\sin }^{-1}}\left( \frac{2\sqrt{2}}{3} \right)\].


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