JEE Main & Advanced Sample Paper JEE Main - Mock Test - 5

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

    A) \[(0,\infty )\]                

    B) \[(-\infty ,0)\]

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

    D) None of these

    Correct Answer: A

    Solution :

    Given \[f(x)=\log (1+x)-\frac{2x}{2+x}\]
    \[f'(x)=\frac{1}{1+x}-\frac{(2+x)(2)-2x}{{{(2+x)}^{2}}}\]\[=\frac{1}{1+x}-\frac{4}{{{(2+x)}^{2}}}=\frac{{{(2+x)}^{2}}-4-4x}{(1+x){{(2+x)}^{2}}}\]\[=\frac{{{x}^{2}}}{(1+x){{(2+x)}^{2}}}>0\] for all \[x\in (0,\infty )\]
    Thus, given function f(x) is increasing on \[(0,\infty )\].


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