JEE Main & Advanced Mathematics Circle and System of Circles Question Bank Equations of circle, Geometrical problems regarding circle

  • question_answer
    A point P moves in such a way that the ratio of its distance from two coplanar points is always a fixed number\[(\ne 1)\]. Then its locus is                                                                      [IIT 1982]

    A)            Straight line                              

    B)            Circle

    C)            Parabola                                   

    D)            A pair of straight lines

    Correct Answer: B

    Solution :

               Let two coplanar points are (0, 0) and (a, 0). Under given conditions, we get                    \[\frac{\sqrt{{{x}^{2}}+{{y}^{2}}}}{\sqrt{{{(x-a)}^{2}}+{{y}^{2}}}}=\lambda ,\ (\lambda \ne 1)\]                (where \[\lambda \] is any number)                    \[\Rightarrow {{x}^{2}}+{{y}^{2}}+\left( \frac{{{\lambda }^{2}}}{{{\lambda }^{2}}-1} \right)\text{ }({{a}^{2}}-2ax)=0\],                    which is the equation of a circle.


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