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

  • question_answer
    The locus of a point, such that the sum of the squares of its distances from the planes \[x+y+z=0,\]\[x-z=0\] And \[x-2y+z=0\]is 9, is

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

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

    C) \[{{x}^{2}}+{{y}^{2}}+{{z}^{2}}=9\]

    D) \[{{x}^{2}}+{{y}^{2}}+{{z}^{2}}=12\]

    Correct Answer: C

    Solution :

    [c] Let the variable point be \[(\alpha ,\beta ,\gamma )\]then according to question \[{{\left( \frac{\left| \alpha +\beta +\gamma  \right|}{\sqrt{3}} \right)}^{2}}+{{\left( \frac{\left| \alpha -\gamma  \right|}{\sqrt{2}} \right)}^{2}}+{{\left( \frac{\left| \alpha -2\beta +\gamma  \right|}{\sqrt{6}} \right)}^{2}}=9\] \[\Rightarrow {{\alpha }^{2}}+{{\beta }^{2}}+{{\gamma }^{2}}=9.\] So, the locus of the point is \[{{x}^{2}}+{{y}^{2}}+{{z}^{2}}=9\]


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