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Differential Area Element

  1. May 29, 2008 #1
    [SOLVED] Differential Area Element

    While doing surface integrals, I am not sure as to which of the following is the correct differential area element to be considered:

    i] [tex]dA = dx dy[/tex]

    or

    ii]
    [tex]A = xy[/tex]

    hence, using the product rule:

    [tex]dA = xdy + ydx[/tex]
     
  2. jcsd
  3. May 29, 2008 #2
    The short answer is simply that [tex]dA = dxdy[/tex]

    Your second equation does not make sense. To use the product rule, you have to differentiate A with respect to either x or y.
     
  4. May 29, 2008 #3
    the first one ... you always start with the infinitesimal element .

    that's not completely correct ..
    if you start with [tex]A=xy[/tex] then [tex]dA=xdy+ydx[/tex] is lgeit .. but we always start with the infinitesimal element when we perform line , surface and volume integrals .
     
    Last edited: May 29, 2008
  5. May 29, 2008 #4
    thanks for the quick replies. I think I get it now...
     
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