JEE Main & Advanced Mathematics Applications of Derivatives Question Bank Maxima and Minima

  • question_answer
    The function \[{{x}^{2}}\log x\]in the interval (1, e) has

    A)            A point of maximum         

    B)            A point of minimum          

    C)            Points of maximum as well as of minimum

    D)            Neither a point of maximum nor minimum

    Correct Answer: D

    Solution :

               Let\[f(x)={{x}^{2}}\log x\]Þ\[f'(x)=2x\log x+x\]                    and \[{f}''(x)=2(1+\log x)+1\]                    Now\[{f}''(1)=3+2{{\log }_{e}}1\]and \[{f}''(e)=3+2{{\log }_{e}}e\]                    \[f(x)\] has local minimum at \[\frac{1}{\sqrt{e}}\], but \[x\]lies only in interval \[(1,e)\] so that \[{{y}_{2}}=\sqrt{x}\] has not extremum in \[(1,e).\]                    Hence neither a point of maximum nor minimum.


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