CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2007

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

    A)  \[-\frac{y}{x}\]                                

    B)  \[-\frac{x}{y}\]

    C)  \[1+\log \left( \frac{x}{y} \right)\]                          

    D)  \[\frac{1+\log x}{1+\log y}\]

    Correct Answer: D

    Solution :

    Given,  \[{{x}^{x}}={{y}^{y}}\] Taking log on both sides, we get \[x\,\log \,x=y\,\log y\] Differentiating w.r.t. y, we get \[y.\frac{1}{y}.\frac{dy}{dx}+\log y\frac{dy}{dx}=x\frac{1}{x}+\log x\] \[\Rightarrow \]               \[\frac{dy}{dx}(1+\log y)=1+\log x\] \[\Rightarrow \]                               \[\frac{dy}{dx}=\frac{1+\log x}{1+\log y}\]


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