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Homework Help: Can't seem to get this DE solved using laplace transforms

  1. Apr 23, 2013 #1
    1. The problem statement, all variables and given/known data

    y''-4y'+4y = 0
    y(0)=1, y'(0)=1

    2. Relevant equations

    3. The attempt at a solution

    This is annoying, because it feels very easy and I don't know why I am not getting the answer. Skipping the routine:

    s^2L{y} - s - 1 - 4sL{y} + 4 + 4L{y} = 0

    (s+3) / (s^2 - 4s + 4) = L{y}

    = s/(s-2)^2 + 3/(s-2)^2

    = 1/(s-2) + 2(1/(s-2)^2) +3(1/(s-2)^2)

    = 5(1/(s-2)^2) + 1/(s-2)

    The inverse transform of which gives:

    5te^2t + e^2t = (5t+1)e^2t

    Any ideas?

  2. jcsd
  3. Apr 23, 2013 #2
    NVM, I think it should be s-3 in num now.
  4. Apr 23, 2013 #3


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    Staff Emeritus
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    Check your signs.

    EDIT: Ah, I see you found the mistake.
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