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Math Help - Cylindrical shells method:

  1. #1
    Senior Member
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    Cylindrical shells method:

    The region bounded by the line y = 1 and the parabola x^2 = 4y
    is revolved about the line y = 1.....
    Take the rectangular elements of area parallel to the axis of revolution


    I set :
    radius = 1 - y
    height = 2\sqrt{y} - (-2\sqrt{y})

    2\pi \int_{-2}^{2} (2\sqrt{y} - (-2\sqrt{y})(1 - y)dy

    2\pi \int_{-2}^{2} (4\sqrt{y})(1 - y)dy

    i need help
    my answer seems to be undefined...
    Last edited by ^_^Engineer_Adam^_^; September 26th 2007 at 07:58 AM.
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  2. #2
    MHF Contributor
    Joined
    Apr 2005
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    The limits of your integration should be y=0 and y=1.

    You are using dy, not dx.
    dy goes from y=0 to y=1.
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