JEE Main & Advanced Mathematics Applications of Derivatives Question Bank Maxima and Minima

  • question_answer
    The point \[(0,\,5)\]is closest to the curve \[{{x}^{2}}=2y\] at            [MNR 1983]

    A)            \[(2\sqrt{2},0)\]

    B)            (0, 0)

    C)            \[(2,\,2)\]

    D)            None of these

    Correct Answer: D

    Solution :

               Let a point on the curve by (h, k)                    Then \[{{h}^{2}}=2k\]                                 ?..(i)                    Distance = D = \[\sqrt{{{h}^{2}}+{{(k-5)}^{2}}}\]                    By (i); \[D=\sqrt{2k+{{(k-5)}^{2}}}\]                    \[\frac{dD}{dk}=\frac{1}{2\sqrt{2k+{{(k-5)}^{2}}}}\times 2(k-5)+2=0\]\[x\in (-1,\infty )\]                    So, at \[k=4\] function D must be minimum.                    Then point will be \[(\pm \,2\sqrt{2},\,4)\].


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