JEE Main & Advanced Sample Paper JEE Main Sample Paper-3

  • question_answer
    If \[y={{\tan }^{-1}}\left( \frac{{{2}^{x}}}{1+{{2}^{2x+1}}} \right),\]then \[\frac{dy}{dx}\]at \[x=0\]is:

    A)  \[-\frac{3}{5}\log 2\]                     

    B)  \[\frac{2}{5}\log 2\]

    C)  \[-\frac{3}{2}\log 2\]                     

    D)  None

    Correct Answer: A

    Solution :

     \[y={{\tan }^{-1}}\left[ \frac{{{2}^{x}}(2-1)}{1+{{2}^{x}}{{.2}^{x+1}}} \right]={{\tan }^{-1}}\left[ \frac{{{2}^{x+1}}-{{2}^{x}}}{1+{{2}^{x}}{{.2}^{x+1}}} \right]\] \[={{\tan }^{-1}}({{2}^{x+1}})-{{\tan }^{-2}}({{2}^{x}})\Rightarrow \frac{dy}{dx}=\frac{{{2}^{x+1}}\log 2}{1+{{2}^{2(x+1)}}}-\frac{{{2}^{x}}\log 2}{1+{{2}^{2x}}}\]\[\therefore \]\[{{\left( \frac{dy}{dx} \right)}_{x=0}}=(\log 2)\left( \frac{2}{5}-1 \right)=\log 2\left( -\frac{3}{5} \right)\]


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