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Laplace last one please check

  1. Apr 25, 2004 #1
    Find laplace transfom (t-1)cos3t + e^(2t)sin4t

    f(t) = t*cos(3*t)
    g(t) = -cos(3*t)
    h(t) = e2*t*sin(4*t)


    int e^(-st) * t* cos(3*t)dt = s^(2)-9/(s^(2)+9)^2
    g(t)= -1/(s^2+9)
    h(t)= (s-2)/(s-2)^2 +16

    am I done and right? Thanks
     
  2. jcsd
  3. Apr 25, 2004 #2

    Tom Mattson

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    The first one is right. The second one is close (you forgot to multiply by 9). The third one looks way off.

    In general, L{ebtsin(at)}=a/[(s-b)2+a2]
     
  4. Apr 25, 2004 #3
    Thanks,

    The third one should be 4/(s-2)^2+16. Do I have to combine all of these. Am unsure about that part.

    Thanks
     
  5. Apr 27, 2004 #4

    Tom Mattson

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    You only have to combine them if the problem says so.

    Did they ask you to find L{f(t)+g(t)+h(t)}?

    If not, then you can leave them seperate.
     
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