JEE Main & Advanced Sample Paper JEE Main Sample Paper-39

  • question_answer
    If \[y={{\log }_{2}}\{{{\log }_{2}}(x)\},\]then\[\frac{dy}{dx}\]is

    A)  \[\frac{{{\log }_{2}}e}{x\,lnx}\]                  

    B)  \[\frac{2.3026}{x\ln \,\,xln\,2}\]

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

    D)  None of these

    Correct Answer: A

    Solution :

     \[y={{\log }_{2}}\{{{\log }_{2}}(x)\}={{\log }_{2}}\{{{\log }_{e}}x.{{\log }_{2}}e\}\] \[\Rightarrow y={{\log }_{e}}\{{{\log }_{e}}x.{{\log }_{2}}e\}.{{\log }_{2}}e\] \[\Rightarrow \] \[\frac{dy}{dx}={{\log }_{2}}e\frac{d}{dx}[{{\log }_{e}}\{{{\log }_{e}}x.{{\log }_{2}}e\}]\] \[\Rightarrow \] \[\frac{dy}{dx}={{\log }_{2}}e.\frac{1}{{{\log }_{e}}x.{{\log }_{2}}e}.({{\log }_{e}}x.{{\log }_{2}}e)\] \[\Rightarrow \] \[\frac{dy}{dx}=\frac{1}{{{\log }_{e}}x}{{\log }_{2}}=\frac{{{\log }_{2}}e}{x\ln x}\]


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