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Homework Help: Laplace transform with time shift

  1. Sep 20, 2010 #1
    1. The problem statement, all variables and given/known data

    I need to find the Laplace transform of t*e-t*u(t-tau)

    2. Relevant equations and attempt at solution

    I know the general form of the transform, but my problem is in the time shift of the step function. If both parts of the expression were (t-tau), then I could just pull out an e(s*tau), but I have no idea what I'm supposed to do when one part has it and the other does not.

    Can anyone help get me started?
     
  2. jcsd
  3. Sep 20, 2010 #2

    vela

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    Hint:

    [tex]te^{-t} = (t-\tau+\tau)e^{-(t-\tau+\tau)}[/tex]
     
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