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Integration: Washer and shell method

  1. Jan 31, 2010 #1
    Hi Everyone

    I am having a trouble setting up an equation: I am to find the volume by integrating the equation y = 4-e^x from 0 to 3 and rotate it about the axis of x = 10.

    Here is what I have:

    the equation y= 4-e^x in terms of x is x = ln(4-y)

    R(y) = 10
    r(y) = ln(4-y)

    the equation I have using the disk method is this:

    v = 2pi integrate from 0 to 3 (10^2)-(ln(4-y))^2)dy

    using the shell method I have (which I think is correct):

    v = 2pi integrate from 0 to ln4 (10-x)(4-e^x)dx
  2. jcsd
  3. Jan 31, 2010 #2
    Wait...I figured it out. :biggrin:
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