J & K CET Engineering J and K - CET Engineering Solved Paper-2008

  • question_answer
    The radius of the sphere \[{{x}^{2}}+{{y}^{2}}+{{z}^{2}}=x+2y+3z\]is

    A)  \[\frac{\sqrt{14}}{2}\]

    B)  \[\sqrt{7}\]

    C)  \[\frac{7}{2}\]

    D)  \[\frac{\sqrt{7}}{2}\]

    Correct Answer: A

    Solution :

    Given equation of sphere is \[{{x}^{2}}+{{y}^{2}}+{{z}^{2}}-x-2y-3z=0\] \[\therefore \]  Centre is \[\left( \frac{1}{2},1,\frac{3}{2} \right).\] \[\therefore \]  Radius \[=\sqrt{{{\left( \frac{1}{2} \right)}^{2}}+{{(1)}^{2}}+{{\left( \frac{3}{2} \right)}^{2}}-0}\] \[=\sqrt{\frac{1}{4}+1+\frac{9}{4}}=\sqrt{\frac{14}{4}}\] \[=\frac{\sqrt{14}}{2}\]


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