CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2001

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

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

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

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

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

    E)  \[\frac{1+\log x}{\log x}\]

    Correct Answer: D

    Solution :

    \[{{x}^{y}}={{e}^{x-y}}\] \[\Rightarrow \]               \[y\log x=(x-y)\] On differentiating w. r. t.\[x,\]we get \[\Rightarrow \]\[y\frac{1}{x}+\log x\frac{dy}{dx}=1-\frac{dy}{dx}\] \[\Rightarrow \]\[\frac{dy}{dx}(1+\log x)=1-\frac{y}{x}\] \[\Rightarrow \]\[\frac{dy}{dx}=\frac{x-y}{x(1+\log x)}=\frac{y\log x}{x(1+\log x)}\]                                                 \[(\because x-y=y\log x)\]


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