JEE Main & Advanced Sample Paper JEE Main Sample Paper-11

  • question_answer
    The acute angle which the line of intersection of the planes 2x + y + z = 0 and x + y + 2z = 0 makes with the positive x-axis, is

    A)  \[{{\tan }^{-1}}\sqrt{8}\]                             

    B)  \[{{\tan }^{-1}}\sqrt{3}\]

    C)  \[{{\tan }^{-1}}\sqrt{10}\]                          

    D)  \[{{\tan }^{-1}}\sqrt{2}\]

    Correct Answer: C

    Solution :

     Vector\[\text{\vec{V}}\]along the line of intersection of the given planes is \[\text{\vec{V}=}\left| \begin{matrix}    {\hat{i}} & {\hat{j}} & {\hat{k}}  \\    2 & 1 & 1  \\    1 & 1 & 2  \\ \end{matrix} \right|=\hat{i}(2-1)-\hat{j}(4-1)+\hat{k}(2-1)\] \[=\hat{i}-3\hat{j}+\hat{k}\] \[\vec{u}=\hat{i},\therefore \cos \theta =\frac{1}{\sqrt{11}};\theta ={{\tan }^{-1}}\sqrt{10}\]


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