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

  • question_answer
    Chord AB is a diameter of the sphere \[\left| \vec{r}-2\vec{i}-\vec{j}+6\vec{k} \right|=\sqrt{18.}\] if the coordinates of A are (3, 2,-2), then the coordinates of B are

    A) (1, 0, 10)

    B) (1, 0, -10)

    C) (-1, 0, 10)

    D) None of these

    Correct Answer: B

    Solution :

    The equation of the sphere is \[\left| r-2\vec{i}-\vec{j}+6\vec{k} \right|=\sqrt{18}\] \[\Rightarrow \]Its centre is at the point\[(\vec{r}-2\vec{i}-\vec{j}+6\vec{k})\], i.e, at \[(2,1,-6).\] coordinates of A are\[(3,2,-2)\]. Let the coordinates of B be\[(\alpha ,\beta ,\gamma )\]. Then, \[\frac{3+\alpha }{2}=2,\frac{2+\beta }{2}=1\] and \[\frac{-2+\lambda }{2}=-6\] \[\Rightarrow \alpha =1,\beta =0,\lambda =-10\] Therefore, coordinates of B are \[(1,0,-10).\]


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