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Homework Help: Help with solid of revolution volume question

  1. Feb 4, 2014 #1
    1. The problem statement, all variables and given/known data

    The problem is attached in this post.

    2. Relevant equations

    The problem is attached in this post.

    3. The attempt at a solution

    I used washer method and set my outer radius as 2+2+√(x-1) and my inner radius as 2. I set my upper limit as 5 and my lower limit as 2.

    I set my integral as π∫((4+√(x-1))^2-(4) dx, from 2 to 5 = 485π/6 which is incorrect, the actual answer is 157π/6.

    Attached Files:

  2. jcsd
  3. Feb 4, 2014 #2
    Hi student93!

    Why do you set the outer radius to 2+2+√(x-1)? Outer radius is simply 2+√(x-1), do you see why?
  4. Feb 4, 2014 #3
    Could you please explain why that's the value of the outer radius? Also is the value of my inner radius correct?
  5. Feb 4, 2014 #4
    Draw a graph and select a disk, it becomes clear why the outer radius is that.
    Yes. :)
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