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

  • question_answer
    The function \[f(x)=\log (1+x)-\frac{2x}{2+x}\]is increasing on                                                               [EAMCET 2002]

    A)            (0, \[\infty \])

    B)            (\[-\infty \], 0)

    C)            \[(-\infty ,\infty )\]

    D)            None of these

    Correct Answer: A

    Solution :

               \[f(x)=\log (1+x)-\frac{2x}{2+x}\]\[\Rightarrow f'(x)=\frac{1}{1+x}-\frac{(2+x).(2-2x)}{{{(2+x)}^{2}}}\]                                                        Þ \[f'(x)=\frac{{{x}^{2}}}{(x+1){{(x+2)}^{2}}}\]                    Obviously, \[f'(x)>0\]for all \[x>0\]                    Hence \[f(x)\]is increasing on \[(0,\infty )\].


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