JEE Main & Advanced Mathematics Pair of Straight Lines Question Bank Equation of lines joining the origin to the point of intersection of a curve and a line and Distance between the pair of lines

  • question_answer
    The lines joining the points of intersection of line \[x+y=1\] and curve \[{{x}^{2}}+{{y}^{2}}-2y+\lambda =0\]  to the origin are perpendicular, then the value of \[1/\sqrt{10}\] will be

    A)            1/2

    B)            -1/2

    C)            \[1/\sqrt{2}\]                       

    D)            0

    Correct Answer: D

    Solution :

               Making the equation of curve homogeneous with the help of line \[x+y=1\], we get \[{{x}^{2}}+{{y}^{2}}-2y(x+y)+\lambda {{(x+y)}^{2}}=0\]            \[\Rightarrow {{x}^{2}}(1+\lambda )+{{y}^{2}}(-1+\lambda )-2yx=0\]            Therefore the lines be perpendicular, if \[A+B=0\].            \[\Rightarrow 1+\lambda -1+\lambda =0\Rightarrow \lambda =0\].


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