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

  • question_answer
    Maximum value of \[x{{(1-x)}^{2}}\] when \[0\le x\le 2\], is [MP PET 1997]

    A)            \[\frac{2}{27}\]                   

    B)            \[\frac{4}{27}\]

    C)            5    

    D)            0

    Correct Answer: B

    Solution :

               Given \[f(x)=x{{(1-x)}^{2}}\], \[f(x)={{x}^{3}}-2{{x}^{2}}+x\]                    Now \[f'(x)=3{{x}^{2}}-4x+1\]                    Put \[f'(x)=0\] i.e., \[3{{x}^{2}}-4x+1=0\]                    \[3{{x}^{2}}-3x-x+1=0\] Þ \[x=1,\,\,1/3\]                    \[{f}''(x)=6x-4\]                    \[\therefore {f}''\,(1)=2=\] positive and \[f''(1/3)=-2=\]?ve                    Hence maximum value will be at \[x=\frac{1}{3}\]                    Maximum value \[f\,\left( \frac{1}{3} \right)=\frac{4}{27}\].


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