JEE Main & Advanced Mathematics Circle and System of Circles Question Bank Tangent and normal to a circle

  • question_answer
    The locus of a point which moves so that the ratio of the length of the tangents to the circles \[{{x}^{2}}+{{y}^{2}}+4x+3=0\] and \[{{x}^{2}}+{{y}^{2}}-6x+5=0\] is 2:3  is                                                               [Kerala (Engg.) 2005]

    A)            \[5{{x}^{2}}+5{{y}^{2}}-60x+7=0\]                             

    B)            \[5{{x}^{2}}+5{{y}^{2}}+60x-7=0\]

    C)            \[5{{x}^{2}}+5{{y}^{2}}-60x-7=0\]                               

    D)            \[5{{x}^{2}}+5{{y}^{2}}+60x+7=0\]

    E)            \[5{{x}^{2}}+5{{y}^{2}}+60x+12=0\]

    Correct Answer: D

    Solution :

               Let the point be\[({{x}_{1}},{{y}_{1}})\]            According to question, \[\frac{\sqrt{x_{1}^{2}+y_{1}^{2}+4{{x}_{1}}+3}}{\sqrt{x_{1}^{2}+y_{1}^{2}-6{{x}_{1}}+5}}=\frac{2}{3}\]            Squaring both sides, \[\frac{x_{1}^{2}+y_{1}^{2}+4{{x}_{1}}+3}{x_{1}^{2}+y_{1}^{2}-6{{x}_{1}}+5}=\frac{4}{9}\]            Þ \[9{{x}_{1}}+9y_{1}^{2}+36{{x}_{1}}+27=4x_{1}^{2}+4y_{1}^{2}-24{{x}_{1}}+20\]            Þ \[5x_{1}^{2}+5y_{1}^{2}+60{{x}_{1}}+7=0\]                    Hence, locus is\[5{{x}^{2}}+5{{y}^{2}}+60x+7=0\].


You need to login to perform this action.
You will be redirected in 3 sec spinner