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

  • question_answer
    The co-ordinates of the foot of perpendicular from the point (2, 3) on the line \[x+y-11=0\]are       [MP PET 1986]

    A)            \[(-6,\,5)\]                                

    B)            \[(5,\,6)\]

    C)            \[(-5,\,6)\]                                

    D)            \[(6,\,5)\]

    Correct Answer: B

    Solution :

               Equation of perpendicular on the line \[x+y-11=0\] is \[x-y+\lambda =0\], but it passes through (2, 3), so \[\lambda =1\].                    Equation of perpendicular is \[x-y+1=0\]. Now the coordinates of the foot of the perpendicular are the intersection point of the lines, hence point is (5, 6).               Aliter : Apply the formula given in the theory part of this book, we get required foot as                 \[\left( \frac{{{1}^{2}}\times 2-1\times 1\times 3-1\times (-11)}{{{1}^{2}}+{{1}^{2}}},\frac{{{1}^{2}}\times 3-1\times 1\times 2-1(-11)}{{{1}^{2}}+{{1}^{2}}} \right)\]                    \[=\left( \frac{2-3+11}{2},\frac{3-2+11}{2} \right)=(5,\,6)\].


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