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Percent increase/decrease cylinder (no values)

  1. Feb 6, 2010 #1
    By approximately what percent would the volume of a right circular cylinder increase or decrease if the height were to increase by 2% and the radius of the base were to decrease by 1.5%?

    Partial differentials makes sense in this case, I am just stuck when I have no usable values.

    Volume of a cylinder = [tex]\pi[/tex]r2h
    dV = [tex]\pi[/tex]r2dh + 2[tex]\pi[/tex]r dr

    dh = 1.02
    dr = .985

    I'm stuck in how to translate this in a comparable way to the original cylinder. Any suggestions are welcome!
     
  2. jcsd
  3. Feb 6, 2010 #2

    rock.freak667

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    Recheck your expression for dV.

    When you do that divide the left side by V and the right side by πr2h and then you can find the percentage.
     
  4. Feb 6, 2010 #3

    Dick

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    No, no. dh isn't 1.02, dh/h is 0.02. And the quantity you want to find is the percentage change. That's dV/V.
     
  5. Feb 6, 2010 #4
    Okay, the only reason I did 1.02 is because I thought of doing I could express is as a negative/positive percentage. This was obviously a bad move and doesn't make any sense. But I got it now. Thanks for the help everyone!
     
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