JEE Main & Advanced Mathematics Three Dimensional Geometry Question Bank Sphere

  • question_answer
    Co-ordinate of a point equidistant from the points (0,0,0), (a, 0, 0), (0, b, 0), (0, 0, c) is [RPET 2003]

    A)            \[\left( \frac{a}{4},\frac{b}{4},\frac{c}{4} \right)\]

    B)            \[\left( \frac{a}{2},\frac{b}{4},\frac{c}{4} \right)\]

    C)            \[\left( \frac{a}{2},\frac{b}{2},\frac{c}{2} \right)\]

    D)            (a, b, c)

    Correct Answer: C

    Solution :

                       The required point is the centre of the sphere through the given points.            Let the equation of sphere be            \[{{x}^{2}}+{{y}^{2}}+2ux+2vy+2wz+d=0\]                               .....(i)            Sphere (i) is passing through (0, 0, 0), (a, 0, 0), (0, b, 0) and (0, 0, c), \[\therefore \,\,d=0\]                    \[{{a}^{2}}+2ua=0\Rightarrow u=-a/2\]                    \[{{b}^{2}}+2vb=0\,\,\Rightarrow \,\,v=-b/2\]                    \[{{c}^{2}}+2wc=0\,\Rightarrow w=-c/2\]            Therefore, centre of sphere is \[(a/2,\,b/2,\,c/2)\], which is also the required point.


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