JEE Main & Advanced JEE Main Solved Paper-2017

  • question_answer
    If for \[x\in \left( 0,\frac{1}{4} \right),\]the derivative of \[{{\tan }^{-1}}\left( \frac{6x\sqrt{x}}{1-9{{x}^{3}}} \right)\]is \[\sqrt{x}.g(x),\]then \[g(x)\]equals:-       JEE Main Solved Paper-2017

    A)  \[\frac{3}{1+9{{x}^{3}}}\]                           

    B)  \[\frac{9}{1+9{{x}^{3}}}\]

    C)  \[\frac{3x\sqrt{x}}{1-9{{x}^{3}}}\]                          

    D)  \[\frac{3x}{1-9{{x}^{3}}}\]

    Correct Answer: B

    Solution :

     Let \[y={{\tan }^{-1}}\left( \frac{6x\sqrt{x}}{1-9{{x}^{3}}} \right)\]where \[x\in \left( 0,\frac{1}{4} \right)\]                 \[={{\tan }^{-1}}\left( \frac{2.(3{{x}^{3/2}})}{1-(3{{x}^{3/2}})} \right)=2{{\tan }^{-1}}(3{{x}^{3/2}})\]                 As           \[3{{x}^{3/2}}\in \left( 0,\frac{3}{8} \right)\] \[\therefore \]  \[g(x)=\frac{9}{1+9{{x}^{3}}}\]


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