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Homework Help: Rotating integrals and circles

  1. Oct 5, 2006 #1
    kay had a question which i got zero on and now trying to figure out how the hell to do the question.

    Given x^2 + (y-1)^2 =1 rotated about the x-axis.

    if i could get the solution so i can review it so i can have a better idea how to do it on the mid term.

    Hint:, I was told to do with respect to the y-axis.
  2. jcsd
  3. Oct 5, 2006 #2


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    So how do you set up the integral?
  4. Oct 5, 2006 #3
    well that part of the stuff that confused me.

    I set it upas
    x = sqrt(1- (y-1)^2)

    so my intergral becomes

    from 0-2 2(pi) y sqrt(2y - Y^2).

    but given that. we end up with a nasty integration... I tryed to get help form soem one but we vouldn't figure it out..
  5. Oct 5, 2006 #4


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    That's right. Try the substitution u=y-1. You'll end up with the sum of two integrals, one you can do by another substitution and the other you can do just knowing the area of a circle.
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