RAJASTHAN ­ PET Rajasthan PET Solved Paper-2007

  • question_answer
    Let\[f:R\to R\]is a differentiable function\[f(2)=6,f'(x)=\frac{1}{48},\]then\[\underset{x\to 2}{\mathop{\lim }}\,\int_{6}^{f(x)}{\frac{4{{t}^{3}}}{x-2}}dt\]is equal to

    A)  24               

    B)  36

    C)  12               

    D)  18

    Correct Answer: D

    Solution :

     \[\underset{x\to 2}{\mathop{\lim }}\,\int_{6}^{f(x)}{\frac{4{{t}^{3}}}{x-2}}dt=\underset{x\to 2}{\mathop{\lim }}\,\frac{\int_{6}^{f(x)}{4{{t}^{3}}dt}}{x-2}\] \[=\underset{x\to 2}{\mathop{\lim }}\,\frac{4{{[f(x)]}^{3}}}{1}f'(x)=4{{[f(2)]}^{3}}.f(2)\] \[=4{{(6)}^{3}}.\left( \frac{1}{48} \right)=18\]


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