JCECE Engineering JCECE Engineering Solved Paper-2006

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

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

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

    C)  not defined                      

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

    Correct Answer: D

    Solution :

    \[{{x}^{y}}={{e}^{x-y}}\] Taking log on both sides, we get                         \[y\log x=x-y\] \[\Rightarrow \]               \[y(\log x+1)=x\] \[\Rightarrow \]                               \[y=\frac{x}{1+\log x}\] On differentiating w.r.t\[x,\] we get \[\Rightarrow \]               \[\frac{dy}{dx}=\frac{(1+\log x)-x\times \frac{1}{x}}{{{(1+\log x)}^{2}}}\] \[\Rightarrow \]               \[\frac{dy}{dx}=\frac{\log x}{{{(1+\log x)}^{2}}}\]


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