JEE Main & Advanced Mathematics Three Dimensional Geometry Question Bank Self Evaluation Test - Introduction to Three Dimensional Geometry

  • question_answer
    The equation of locus of a point whose distance from the y-axis is equal to its distance from the point (2, 1, -1) is

    A) \[{{x}^{2}}+{{y}^{2}}+{{z}^{2}}=6\]

    B) \[{{x}^{2}}-4x+2z+6=0\]

    C) \[{{y}^{2}}-2y-4x+2z+6=0\]

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

    Correct Answer: C

    Solution :

    [c] The variable point is \[P(x,y,z)\]. Its distance from the y-axis \[=\sqrt{{{x}^{2}}+{{z}^{2}}}\] Its distance from (2, 1, -1) \[=\sqrt{{{(x-2)}^{2}}+{{(y-1)}^{2}}+{{(z+1)}^{2}}}\] Given: \[\sqrt{{{x}^{2}}+{{z}^{2}}}=\sqrt{{{(x-2)}^{2}}+{{(y-1)}^{2}}+{{(z+1)}^{2}}}\] \[\Rightarrow \,\,\,\,{{y}^{2}}-2y-4x+2z+6=0\]


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