JEE Main & Advanced JEE Main Paper (Held On 9 April 2017)

  • question_answer
    If a variable plane, at a distance of 3 units from the origin, intersects the coordinate axes at A, B and C, then the locus of the centroid of \[\Delta ABC\] is.         [JEE Online 09-04-2017]

    A)  \[\frac{1}{{{x}^{2}}}+\frac{1}{{{y}^{2}}}+\frac{1}{{{z}^{2}}}=1\]

    B)  \[\frac{1}{{{x}^{2}}}+\frac{1}{{{y}^{2}}}+\frac{1}{{{z}^{2}}}=3\]

    C) \[\frac{1}{{{x}^{2}}}+\frac{1}{{{y}^{2}}}+\frac{1}{{{z}^{2}}}=9\]

    D)  \[\frac{1}{{{x}^{2}}}+\frac{1}{{{y}^{2}}}+\frac{1}{{{z}^{2}}}=\frac{1}{9}\]

    Correct Answer: A

    Solution :

    Let Centroid be \[(h,\,k,\,l)\] \[\therefore \,\,\,x-\,\text{intp}\,\,\text{=3h}\,\,\,\,\,\text{Y-intp}\,\text{=3k,}\,\,\text{3-int}\,\,\text{= 3l}\] Equ.       \[\frac{x}{3h}+\frac{y}{3k}+\frac{z}{3\ell }=1\] dist from \[(0,0,0)\] \[\left| \frac{-1}{\sqrt{\frac{1}{9{{h}^{2}}}+\frac{1}{9{{k}^{2}}}+\frac{1}{9{{l}^{2}}}}} \right|=3\] \[=1\]


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