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Homework Help: Need help with inverse laplace transformation

  1. Nov 27, 2008 #1
    1. The problem statement, all variables and given/known data
    (s^3+6s^2-18s+13)/(s(s+1)(s^2-4s+13)


    2. Relevant equations



    3. The attempt at a solution
    I am so lost on this problem. I have tried it several times and just keep confusing myself. I think that I am messing up jsut setting up the problem. Can someone please help me out? How do I get this into partial fraction and then where do I go from there.
     
  2. jcsd
  3. Nov 28, 2008 #2
    Hi Karmel,

    Assuming you want to take the inverse Laplace transform of F(s) = (s^3+6s^2-18s+13)/(s(s+1)(s^2-4s+13)), the first step is to decompose it into partial fractions, which I'm sure you would have come across before. There are three such partial fractions, of the form A/s, B/(s+1) and (Cs+D)/(s^2-4s+13), with A, B, C and D constants to be determined.

    Show us your work so we know where you're getting stuck.
     
  4. Nov 30, 2008 #3
    I would love to show my work but after I set it up like showed to me above with the partial fraction I dont know what to do. The book I am using is so unclear on partial fractions. What are the steps?
     
  5. Dec 1, 2008 #4
    so after doing the partial fractions if I am doing it right I get teh final answer to be

    1-e^-s+(s+4)(sin(3s)(e2s)/3)

    I really hope that is right cause I have tried it a thousand ways and Iam getting no where....
     
  6. Dec 2, 2008 #5

    Defennder

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    Homework Helper

    You can check your answer using this online calculator:

    http://wims.unice.fr/wims/wims.cgi?session=COB95DF175.3&+lang=en&+module=tool%2Fanalysis%2Ffourierlaplace.en [Broken]

    I don't know if that link would expire over time, but if it does, just head to the main page and look for the online Fourier-Laplace calculator. Apart from that I'm kind of lazy to work it out.
     
    Last edited by a moderator: May 3, 2017
  7. Jan 8, 2010 #6
    (s^2+2s+1)/(s^3+2s^2+4s+2)
     
  8. Jan 9, 2010 #7
    (s^2+2s+1)/(s^3)+2(s^2)+4s+2)
     
  9. Jan 9, 2010 #8
    (s^2+2s+1)/((s^3)+2(s^2)+4s+2)
     
  10. Dec 12, 2010 #9
    can anyone help with this
    s((s-a)^0.5)
     
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