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Homework Help: Prerequisites for Laplace Transforms

  1. Jun 30, 2010 #1
    Hi, I was wondering what the prerequisites are for doing Laplace Transforms. I'm just a little confused with one of the examples :

    [tex]\int_0^{\infty} = e^{-sx} dx = [e^{-sx}/s]_0^{\infty} = 1/s[/tex]

    I understand that [tex]e^{-s(0)}[/tex] is 1. But where does the [tex]e^{-s(\infty)}[/tex] part go? Is there something I should cover before this, in the book I have, the chapters before Laplace transforms that I haven't done are Double Integration, Triple Integration, Beta and Gamma Functions.
  2. jcsd
  3. Jun 30, 2010 #2
    regarding your first doubt [itex] e^{-s\infty} =e^{-\infty}[/itex] because anything multiplied with infinity is again infinity and
    [itex] e^{-\infty}=0[/itex]
  4. Jun 30, 2010 #3
    Oh my, I forgot I was dealing with a negative power! Of course:

    [tex] e^{-\infty} = 1/e^{\infty} = 0[/tex]

    Just one of those mental blocks! Thanks n.karthick.
  5. Jun 30, 2010 #4


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    You have to be careful about domains, make sure that you have a half infinite domain before you can apply it.

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