Manipal Engineering Manipal Engineering Solved Paper-2009

  • question_answer
    If\[f:[2,\,\,3]\to R\] is defined by\[f(x)={{x}^{3}}+3x-2\], then the range\[f(x)\]is contained in the interval

    A) \[[1,\,\,12]\]                     

    B) \[[12,\,\,34]\]

    C) \[[35,\,\,50]\]   

    D)        \[[-12,\,\,12]\]

    Correct Answer: B

    Solution :

    Given,\[f(x)={{x}^{3}}+3x-2\] On differentiating w.r.t. x, we get, \[f(x)=3{{x}^{2}}+3\] Put         \[f(x)=0\]  \[\Rightarrow \]  \[3{{x}^{2}}+3=0\] \[\Rightarrow \]               \[{{x}^{2}}=-1\] \[\therefore \] \[f(x)\]is either increasing or decreasing. At\[x=2,\,\,f(2)={{2}^{3}}+3(2)-2=12\] At\[x=3,\,\,f(3)={{3}^{3}}+3(3)-2=34\] \[\therefore \]\[f(x)\in [12,\,\,34]\]


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