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Homework Help: Difficulty with washer method when revolving around axis other than y or x axis.

  1. Sep 10, 2007 #1


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    1. The problem statement, all variables and given/known data
    The region in the second quadrant bounded above by the curve y=-x^3, below by the x-axis, and on the left by the line x=-1, about the line x=-2

    2. Relevant equations

    It's basically the big radius squared minus the small radius squared, integrated in terms of y, and multiply that by pi, I think. But I have a hard time coming up the with expression for that when it's revolved around something other than the x or y axis... Please help?

    3. The attempt at a solution

    Well, the curve in terms of y is x=(-y)^(1/3). I have a hard time adjusting that so it is the right equation for the big radius, and adjusting the x=-1 so it is the small radius....
  2. jcsd
  3. Sep 10, 2007 #2
    Wow that is an interesting washer o.o.

    Well if it's about the line x=-2 and you want to change it to the y -axis. What is the y-axis? x=? how can you change x=-2 to x=(y-axis)?

    also look at a graph of this function. What are the limits? x=-1, and x=? You also need these for when you change x=(y-axis).
    Last edited: Sep 10, 2007
  4. Sep 10, 2007 #3
    wow i'm really confused by this problem. it's been a while since i've done volumes but i figure i could at least get somewhere.

    thinking thinking :)
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