CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2007

  • question_answer
    If\[f(x)=3{{x}^{4}}+4{{x}^{3}}-12{{x}^{2}}+12,\] then\[f(x)\]is

    A)  increasing in\[(-\infty ,-2)\]and in (0, 1)

    B)  increasing in\[(-2,0)\] and in\[(1,\infty )\]

    C)  decreasing in\[(-2,\text{ }0)\]and in (0, 1)

    D)  decreasing in\[(-\infty ,-2)\] and in\[(1,\text{ }\infty )\]

    E)  increasing in\[(-2,\text{ }0)\]and in (0,1)

    Correct Answer: B

    Solution :

    \[\because \]\[f(x)=3{{x}^{4}}+4{{x}^{3}}-12{{x}^{2}}+12\] \[f(x)=12{{x}^{3}}+12{{x}^{2}}-24x\]                 \[=12x({{x}^{2}}+x-2)\]                 \[=12x(x-1)(x+2)\] From above it is clear that \[f(x)\]is increasing in\[(-2,0)\]and in\[(1,\infty )\]


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