1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: 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


    User Avatar
    Science Advisor
    Homework Helper

    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:
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook