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

  • question_answer
    If \[f(x)=\frac{1}{x+1}-\log \,(1+x),\,x>0,\]then \[f\]is  [RPET 2002]

    A)            An increasing function     

    B)            A decreasing function

    C)            Both increasing and decreasing function

    D)            None of these

    Correct Answer: B

    Solution :

               \[f(x)=\frac{1}{x+1}-\log (1+x)\] Þ \[{f}'(x)=-\frac{1}{{{(x+1)}^{2}}}\,-\,\frac{1}{1+x}\]            \[{f}'(x)=-\left[ \frac{1}{x+1}+\frac{1}{{{(x+1)}^{2}}} \right]\]            \[{f}'(x)=-ve\], when \[x>0\]or \[{f}'(x)<0\], \[\forall x>0\]                    \\[f(x)\] is decreasing function.


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