CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2008

  • question_answer
    A point on curve\[x{{y}^{2}}=1\]which is at minimum distance from the origin is

    A)  (1, 1)

    B)  (1/4, 2)

    C)  \[({{2}^{1/6}},{{2}^{-1/3}})\]

    D)  \[({{2}^{-1/3}},{{2}^{1/6}})\]

    E)  None of the above

    Correct Answer: D

    Solution :

    Let\[({{t}^{2}},1/t)\] be a point on the curve. If its distance from origin is\[\lambda ,\]then \[{{\lambda }^{2}}={{t}^{4}}+\frac{1}{{{t}^{2}}}\] \[\Rightarrow \]               \[\frac{d}{dt}({{\lambda }^{2}})=4{{t}^{3}}-\frac{2}{{{t}^{3}}}\] \[\Rightarrow \]               \[\frac{{{d}^{2}}}{d{{t}^{2}}}({{\lambda }^{2}})=12{{t}^{3}}+\frac{6}{{{t}^{4}}}>0\] Now, put\[\frac{d}{dt}({{\lambda }^{2}})=0\Rightarrow t={{2}^{-1/6}}\] Hence, required point is\[({{2}^{-1/3}},{{2}^{1/6}})\].


You need to login to perform this action.
You will be redirected in 3 sec spinner