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

  • question_answer
    What is the equation of the locus of a point which moves such that 4 times its distance from the x-axis is the square of its distance from the origin    [Karnataka CET 2004]

    A) \[{{x}^{2}}+{{y}^{2}}-4y=0\]

    B) \[{{x}^{2}}+{{y}^{2}}-4|y|=0\]

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

    D) \[{{x}^{2}}+{{y}^{2}}-4|x|=0\]

    Correct Answer: B

    Solution :

    Let the required point be \[({{x}_{1}},\,{{y}_{1}})\]. Then, according to question, \[4|{{y}_{1}}|=(x_{1}^{2}+y_{1}^{2})\] Þ \[x_{1}^{2}+y_{1}^{2}-4\,\left| {{y}_{1}} \right|=0\] Replace \[({{x}_{1}},\,{{y}_{1}})\] from \[(x,\,y)\], then \[{{x}^{2}}+{{y}^{2}}-4y=0\] is the required locus.


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