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Homework Help: Volumes using integration

  1. Mar 22, 2013 #1
    1. The problem statement, all variables and given/known data

    Find the volume of the solid formed by revolving the functions: y=x2 and y=1 about the line y=6

    2. Relevant equations


    3. The attempt at a solution

    I found the outer radius to be (1-x2)-6 and my inner radius to be -6. Also, the limits of integration were -1 and 1. Plugging it all in got -224/15. This is obviously wrong because it is negative, and the positive value didn't work either. Does anyone have a clue on how to do this?
  2. jcsd
  3. Mar 22, 2013 #2


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    Isn't the inner radius the distance from y=1 to y=6? Isn't that 5? What's the outer radius?
  4. Mar 23, 2013 #3
    Yes, you are right. I see now, the outer radius will be the distance between y=6 and the lower function and the inner will be the distance between y-6 and the upper function. It worked by the way, thanks.
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