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Homework Help: An approximation for exponential.

  1. Oct 10, 2009 #1
    Is there an approximation for exp(-k*L) with L large but finite??
     
  2. jcsd
  3. Oct 10, 2009 #2

    Hurkyl

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    Well, what is
    [tex]\lim_{L \to +\infty} e^{-kL}[/tex]​
    ? Doesn't calculus tell you that limit would be a good approximation?

    (P.S. are you making any assumptions about k? )
     
  4. Oct 10, 2009 #3
    L is large but finite. No assumptions about k but it is positive.
     
  5. Oct 10, 2009 #4

    Delphi51

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    Homework Helper

    Power series. Use as many terms as you like to improve accuracy.
    I can't seem to do Latex code, but you'll find it here about a screenfull down.
    http://en.wikipedia.org/wiki/Power_series

    Oops - no good for negative exponent!
     
  6. Oct 10, 2009 #5
    The trouble with that is that you can not say that exp(-k*L)=1+-k*L. you need the entire sum.
     
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