JCECE Engineering JCECE Engineering Solved Paper-2002

  • question_answer
    \[\int_{2}^{4}{x}\sqrt{6-x}\,dx\]is equal to:

    A) \[\frac{16}{5}(3-\sqrt{2})\]                         

    B) \[\frac{32}{5}(3-\sqrt{2})\]

    C) \[\frac{8}{5}(3-\sqrt{2})\]                            

    D)  \[\frac{64}{5}(3-\sqrt{2})\]

    Correct Answer: B

    Solution :

    Let          \[I=\int_{3}^{4}{x\sqrt{6-x}dx}\] By using the property \[\therefore \]  \[I=\int_{2}^{4}{(6-x)}\sqrt{x}dx\]                 \[=\int_{2}^{4}{(6{{x}^{1/2}}-{{x}^{3/2}})d}x\]                 \[=\left[ \frac{6{{x}^{3/2}}}{3/2}-\frac{{{x}^{5/2}}}{5/2} \right]_{2}^{4}\]             \[=\left[ 4\times 8-\frac{2}{5}\times 32-\left( 4\times 2\sqrt{2}-\frac{2}{5}\times 4\sqrt{2} \right) \right]\]                 \[=\left[ 32-\frac{64}{5}-\frac{32\sqrt{2}}{5} \right]\]                 \[=\frac{32}{5}(3-\sqrt{2})\]


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