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Math Help - Integration Help

  1. #1
    Newbie
    Joined
    May 2009
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    Integration Help

    What I think I need help with is (forgive my Latex ignorance):
    . . ._____
    √1+1/x dx

    I have no idea how to integrate this.

    In case I set up the integral wrong, the original question calls for evaluating the surface area of y=2√x rotated around the x-axis (on the interval from 4 to 9).

    So first derivative (1/√x)
    First derivative squared (1/x)

    Into the form of (arc length x 2π):
    . . . . ._____
    √1+1/x dx (evaluated on aforementioned interval.)
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  2. #2
    Eater of Worlds
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    Chaneysville, PA
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    Thanks
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    2{\pi}\int_{a}^{b}f(x)\sqrt{1+[f'(x)]^{2}}dx. You forgot the f(x)

    The surface area is given by 4{\pi}\int_{4}^{9}\sqrt{x}\sqrt{1+\frac{1}{x}}dx

    This simplifies down to 4{\pi}\int_{4}^{9}\sqrt{x+1}dx

    Now, can you integrate that. A little easier now?.
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  3. #3
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    Oh yeah! Thanks!
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