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I'm not quite understanding the formation of the radius

  1. Dec 30, 2012 #1
    1. The problem statement, all variables and given/known data
    Use the method of cylindrical shells to find the volume generated by rotating the region bounded by the curves about the specified axis.

    y=x^4, y=0, x=1; about x=2

    2. The attempt at a solution

    I know how to do the problem, except how to find the radius. Like I know if it was about the x axis then the radius would just be x. But since it's about x=2, would the radius be 2-x? If it is 2-x, why?

    I'm guessing it's 2-x because there was a similar problem earlier in the book that showed this being the radius when it was about x=2.
     
  2. jcsd
  3. Dec 30, 2012 #2

    tiny-tim

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    Hi Xetman! :smile:

    (try using the X2 button just above the Reply box :wink:)
    The region is a sort of collar centred around x = 2.

    So your cylindrical shells will also be centred around x = 2 …

    so the radius of the shell that goes through (x,0,0) is the distance of (x,0,0) from (2,0,0). :wink:
     
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