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What p(x) should be in shell method

  1. Feb 9, 2012 #1
    1. The problem statement, all variables and given/known data
    y=x^(1/2) x=4

    find volume of revolution about the line x=4

    this was a test problem and i chose x as p(x) [radius] but now i think that it should've been (x+4).

    :confused:
     
  2. jcsd
  3. Feb 9, 2012 #2

    SammyS

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    I'm confused too !

    What question are you asking?
     
  4. Feb 9, 2012 #3
    In calculus II, graphing a function and then revolving it around an axis. calculate that volume either by disk/washer method or shell method.

    and the formula for the shell method is


    2\pi \int_{a}^{b} (p(y)h(y))\,dy
    o:)
     
  5. Feb 9, 2012 #4

    SammyS

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    Yes, of course! I get that, but what did you mean by
    y=x^(1/2) x=4​

    I'd rather not have to guess when I'm answering someones question.
     
  6. Feb 10, 2012 #5
    it's the region bounded by y = [itex]\sqrt{}x[/itex] and x = 4
     
  7. Feb 10, 2012 #6

    SammyS

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    You need at least one more boundary; perhaps the x-axis ?
     
  8. Feb 10, 2012 #7
    i thought the same thing, y = 0, but it wasn't given. part (a) of the problem was revolution around the x-axis. i just implicitly assumed it was. so what would p(x) be in this region.
     
  9. Feb 10, 2012 #8

    SammyS

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    Assuming that the problem is:
    Find the volume of revolution, using the shell method, if the region bounded by y=x1/2, x=4, and y=0 is revolved about the line x = 4. ​
    The radius is the distance that an arbitrary value of x is from x=4. That distance is |x-4|. Assuming that the integration is done
    from x = 0 to x = 4, then, |x-4| = 4 - x .
     
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