Manipal Engineering Manipal Engineering Solved Paper-2010

  • question_answer
    If\[{{x}^{y}}={{e}^{x}}^{-y}\], then\[\frac{dy}{dx}\]is equal to

    A) \[\frac{\log x}{{{(1+\log x)}^{2}}}\]                         

    B) \[\frac{x-y}{(1+\log x)}\]

    C) \[\frac{x-y}{{{(1+\log x)}^{2}}}\]              

    D)        \[\frac{1}{(1+\log x)}\]

    Correct Answer: A

    Solution :

    We have,\[{{x}^{y}}={{e}^{x-y}}\] \[\Rightarrow \]               \[y\log x=(x-y)\log e=x-y\] \[\Rightarrow \]               \[y=\frac{x}{1+\log x}\] \[\Rightarrow \]               \[\frac{dy}{dx}=\frac{(1+\log x)\cdot 1-x\cdot \frac{1}{x}}{{{(1+\log x)}^{2}}}=\frac{\log x}{{{(1+\log x)}^{2}}}\]


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