J & K CET Engineering J and K - CET Engineering Solved Paper-2005

  • question_answer
    In    the    mean    value    theorem \[f(b)-f(a)=(b-a)\,f'(c),\] if \[a=4,\text{ }b=9\]and     \[f(x)=\sqrt{x},\] then the value of c is

    A)  \[8.00\]          

    B)  \[5.25\]

    C)  \[4.00\]          

    D)  \[6.25\]                     

    Correct Answer: D

    Solution :

    Given,   \[a=4,\,n=9,\,f(x)=\sqrt{x}\] and   \[f(b)-f(a)=(b-a)\,f'(c)\] \[\Rightarrow \] \[f'(c)=\frac{f(b)-f(a)}{b-a}=\frac{3-2}{9-4}\] \[\Rightarrow \] \[f'(c)=\frac{1}{5}\] \[\Rightarrow \] \[\frac{1}{2}{{c}^{-1/2}}=\frac{1}{5}\] \[\Rightarrow \] \[{{c}^{-1/2}}=\frac{5}{2}\] \[\Rightarrow \] \[c={{\left( \frac{5}{2} \right)}^{2}}=\frac{25}{4}=6.25\]


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