JCECE Engineering JCECE Engineering Solved Paper-2012

  • question_answer
    Find the critical points of the function \[f(x)={{(x-2)}^{2/3}}(2x+1)\].

    A)  \[-1\]and\[2\]                 

    B) \[1\]

    C)  \[1\]and\[-\frac{1}{2}\]                               

    D) \[1\]and\[2\]

    Correct Answer: B

    Solution :

    We have,                 \[f(x)={{(x-2)}^{3/2}}(2x+1)\] \[\Rightarrow \]               \[f'(x)=\frac{2}{3}{{(x-2)}^{-1/3}}(2x+1)\]                                                 \[+{{(x-2)}^{2/3}}\cdot 2\]                 \[=\frac{2(2x+1)}{3{{(x-2)}^{1/3}}}+2{{(x-2)}^{2/3}}\]                 \[=\frac{2(2x+1)+6(x-2)}{3{{(x-2)}^{1/3}}}\]                 \[=\frac{4x+2+6x-12}{3{{(x-2)}^{1/3}}}\]                 \[=\frac{10(x-1)}{3{{(x-2)}^{1/3}}}\] For critical points,                 \[f'(x)=0\] \[\Rightarrow \]               \[x=1\] and \[f'(x)\] is not defined at\[x=2.\]


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