JEE Main & Advanced Mathematics Rectangular Cartesian Coordinates Question Bank Transformation of axes and Locus

  • question_answer
    Two points A and B have coordinates (1, 0) and (-1, 0) respectively and Q is a point which satisfies the relation \[AQ-BQ=\]\[\pm 1.\]The locus of Q is [MP PET 1986]

    A) \[12{{x}^{2}}+4{{y}^{2}}=3\]

    B) \[12{{x}^{2}}-4{{y}^{2}}=3\]

    C) \[12{{x}^{2}}-4{{y}^{2}}+3=0\]

    D) \[12{{x}^{2}}+4{{y}^{2}}+3=0\]

    Correct Answer: B

    Solution :

    According to the given condition \[\sqrt{{{(x-1)}^{2}}+{{y}^{2}}}-\sqrt{{{(x+1)}^{2}}+{{y}^{2}}}=\pm 1\] On squaring both sides, we get \[2{{x}^{2}}+2{{y}^{2}}+1=2\sqrt{{{(x-1)}^{2}}+{{y}^{2}}}.\sqrt{{{(x+1)}^{2}}+{{y}^{2}}}\] Again on squaring, we get\[12{{x}^{2}}-4{{y}^{2}}=3\].


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