JEE Main & Advanced Sample Paper JEE Main - Mock Test - 22

  • question_answer
    The image of the point (-1, 3,4) in the plane \[x-2y=0\] is

    A) \[\left( -\frac{17}{3},\,\,-\frac{19}{3},\,\,4 \right)\]

    B)    (15, 11, 4)

    C) \[\left( -\frac{17}{3},\,\,-\frac{19}{3},\,\,1 \right)\]

    D)   None of these

    Correct Answer: D

    Solution :

    If \[\left( \alpha , \beta , \gamma  \right)\] be the image, then mid-point of \[\left( \alpha , \beta , \gamma  \right)\] and (-1, 3, 4) must lie on \[x\text{ }-2y=0\] \[\therefore \,\,\,\frac{\alpha -1}{2}-2\,\left( \frac{\beta +3}{2} \right)=0\] \[\therefore  \,\,\alpha -1-2\beta -6=\,\,0\,\,\Rightarrow \,\, \alpha \,-2\beta =7\]          ... (1) Also line joining \[\left( \alpha , \beta , \gamma  \right)\] and (-1, 3, 4) should be parallel to the normal of the plane \[x-2y=\text{ }0\] \[\therefore \,\,\,\frac{\alpha +1}{1}=\frac{\beta -3}{-\,2}=\frac{\gamma -4}{0}=\lambda \] \[\Rightarrow \,\,\,\alpha =\lambda -1,\,\,\beta =-\,2\lambda +3,\,\,\,\gamma =4\]              ... (2) From (1) and (2) \[\alpha =\frac{9}{5},\,\,\,\beta =-\frac{13}{5},\,\,\gamma =4\] None of the option matches.


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