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Homework Help: Lapalce transformation

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

    Find a Lapalce transformation of
    [tex] cos^2t[/tex]



    2. Relevant equations



    3. The attempt at a solution
    started like this
    [tex]\mathcal{L}(s)=\int_0^{\infty} e^{-st}\cos^2t\mbox{d}t=\frac{1}{2}\int_0^{\infty}e^{-st}(\cos 2t+1)\mbox{d}t=\frac{1}{2}\int_0^{\infty}e^{-st}\cos 2t\mbox{d}t+\frac{1}{2}\int_0^{\infty}e^{-st}\mbox{d}t=...[/tex]
    but i wonder how much the last integral is going to be?
    1. The problem statement, all variables and given/known data
     
  2. jcsd
  3. Sep 1, 2010 #2

    rock.freak667

    User Avatar
    Homework Helper

    ∫e-st=(-1/s)e-st

    Now just put in the limits from ∞ to 0 and you will get the answer easily.
     
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