JEE Main & Advanced Mathematics Straight Line Question Bank Foot of perpendicular, Transformation, Pedal points Image of a point

  • question_answer
    The image of a point \[A(3,\,8)\]in the line \[x+3y-7=0\], is  [RPET 1991]

    A)            \[(-1,-4)\]                                  

    B)            \[(-3\,,\,\,-8)\]

    C)            \[(1,-4)\]                                   

    D)            \[(3,\,8)\]

    Correct Answer: A

    Solution :

               Equation of the line passing through (3, 8) and perpendicular to \[x+3y-7=0\]is \[3x-y-1=0\]. The intersection point of both the lines is (1, 2).                    Now let the image of \[A(3,8)\]be \[{A}'({{x}_{1}},{{y}_{1}}),\]then point (1, 2) will be the midpoint of \[A{A}'\].                    Þ \[\frac{{{x}_{1}}+3}{2}=1\Rightarrow {{x}_{1}}=-1\] and\[\frac{{{y}_{1}}+8}{2}=2\]Þ \[{{y}_{1}}=-4\].                    Hence the image is (?1, ?4).


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