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Homework Help: Shell method versus disk method

  1. May 6, 2008 #1
    I'm confused when to use the shell method vs. the disk method

    Specifically in this problem:

    If the region encolsed by the y-axis, the line y=2 and the curve y=[tex]\sqrt{x}[/tex] is revolved around the y-axis, the volume of the solid generated is:

    However when I use the shell method and the disk method I get different answers

    Can someone tell me what I'm doing wrong?

    Disk Method:
    [tex]\pi[/tex] [tex]\int[/tex]y^4 dy evaluated from 0 to 2

    Shell Method:

    2[tex]\pi[/tex][tex]\int[/tex]x(2-[tex]\sqrt{x}[/tex])dx

    Help please!!
     
  2. jcsd
  3. May 6, 2008 #2

    Vid

    User Avatar

    I got the same answer. Remember the second integral is from 0 to 4 not 0 to 2.
     
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