J & K CET Engineering J and K - CET Engineering Solved Paper-2014

  • question_answer
    If \[y=x{{e}^{2y}},\]then find \[dy/dx\].

    A)  \[y/(x(1-2x))\]     

    B)  \[x/(y\,(1-2x))\]

    C)  \[x/(y(1-2y))\]     

    D)  \[y/(x(1-2y))\]

    Correct Answer: D

    Solution :

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


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