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Multivariable calc help

  1. Jul 22, 2007 #1
    I'm studying calculus III topics on my own, but I've seen this notation prop up a lot. Could you tell me what it means?


    The notation on this page, it has this notation:

    [tex]( \frac{dA}{dx} )_y = ( \frac{dB}{dy} )_x[/tex]

    What do the x's and y's mean as subscript of the parenthesis? Just plug in the y value at that point into that derivative's equation?
  2. jcsd
  3. Jul 22, 2007 #2
    That's a common way of denoting a partial derivative--in other words, if F is a function, then Fx is the partial derivative of F with respect to x.
  4. Jul 22, 2007 #3
    But it's already taking the partial derivative with respect to x, and in the other, y. What's up with that?
  5. Jul 22, 2007 #4
    OH, sorry, actually in that case I think the notation [tex]\left( \frac{\partial A}{\partial y} \right)_{x}[/tex] means "the partial derivative of A with respect to y, holding x constant." See the last example under "Notation" here: http://en.wikipedia.org/wiki/Partial_differential#Notation
  6. Jul 23, 2007 #5
    Thank you.
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