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Homework Help: How to find the new limits of integration

  1. Sep 28, 2011 #1
    1. The problem statement, all variables and given/known data

    I'm confused about a certain aspect of shell method, washer method, and disk method. If I want to rotate using the washer method about the x-axis how do I get the new limits of integration?

    For example: y = 9-x2 over [0,3] about x-axis.
    I solved for x and got: x = sqrt(9-y) but how do I calculate the new limits?
    Also do I need to find the new limits for disk, shell, and washer method in certain cases or is it only for shell and washer?

    I know how to set up and solve the integral it's just calculating the new limits. Any help would be great.
  2. jcsd
  3. Sep 28, 2011 #2


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    Homework Helper

    You are initially given values for x, so when x=0 what is y? Similarly when x=3 what is y?

    (from the equation y=9-x2)

    Those will be your limits.
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