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JEE Main & Advanced Mathematics Applications of Derivatives Question Bank Increasing and Decreasing Function

  • question_answer
    The function \[{{x}^{4}}-4x\]is decreasing in the interval

    A)            [?1, 1]

    B)            \[(-\infty ,\,\,1)\]

    C)            \[[1,\,\,+\infty )\]

    D)            None of these

    Correct Answer: B

    Solution :

               Let \[f(x)={{x}^{4}}-4x\Rightarrow f'(x)=4{{x}^{3}}-4\]                    So, \[4{{x}^{3}}-4<0\]or \[{{x}^{3}}<1\]                    Hence function of decreasing in \[(-\infty ,1)\].


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