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Taylor Expansion of f+df About x?

  1. Oct 17, 2013 #1
    How would one expand f+df about x? I'm messing something up in the process and can't seem to resolve it lol
     
  2. jcsd
  3. Oct 17, 2013 #2

    mfb

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    What does f+df mean?
    How are they related to x?

    There is way too much context missing to answer that.
     
  4. Oct 18, 2013 #3
    It shouldn't matter; f is a function of x (and other variables)...
     
  5. Oct 18, 2013 #4

    pwsnafu

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    You can't Taylor expand around a variable. You expand around a fixed base point. That's why we write the polynomials terms as ##(x-a)^n##, i.e. expand around a.
     
  6. Oct 18, 2013 #5

    mfb

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    It does matter. Letters without any definition are pointless.
    It is like asking "what is x+y?" You cannot answer it (apart from "it is x+y") if you have no idea what x and y are.
     
  7. Oct 22, 2013 #6
    Wow...

    I was either communicating poorly or something. I found my answer.

    f+df = f +(df/dx)dx + (d2f/dx2)dx2 + ... [The parenthetical terms are partials but not the differentials.]

    My favorite is, "It does matter. Letters without any definition are pointless." And to think I wasted all that time learning Algebra! :/
     
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