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

  • question_answer
    The function \[f(x)=1-{{e}^{-{{x}^{2}}/2}}\] is                                     [AMU 1999]

    A)            Decreasing for all x            

    B)            Increasing for all x

    C)            Decreasing for \[x<0\] and increasing for \[x>0\]

    D)            Increasing for \[x<0\] and decreasing for \[x>0\]

    Correct Answer: C

    Solution :

               \[f(x)=1-{{e}^{-{{x}^{2}}/2}}\]            \[{f}'(x)=-{{e}^{-{{x}^{2}}/2}}(-x)=x{{e}^{-{{x}^{2}}/2}}\]            For \[f(x)\] to be increasing, \[{f}'(x)>0\]            Þ \[x{{e}^{-{{x}^{2}}/2}}>0\] Þ \[x>0\] and \[f(x)\] to be decreasing for \[x<0\].


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