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Need help compute the laplace transform

  1. Apr 26, 2005 #1
    need help
    compute the laplace transform of
    h(t)= -5t^2
    I took the integral((-5t^2)e^-(st)) i forgot integration by parts so i did it the hard way in my head and finally got
    lim t -> oo 5[(-1/s)(t^2)(e^-st) - (2te^-st) - (2se^-st)] 0--oo
    i got 10s but the book says -10/s^3
    did i get the inetgration wrong or is it the second part thats wrong

    i also have to verify that L[t^n]= n!/s^(n+1) basicaly the same problem but general
    muchos gracias and stuff
     
  2. jcsd
  3. Apr 26, 2005 #2

    saltydog

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    [tex]\mathcal{L}\{-5t^2\}=-5\int_0^\infty e^{-st}t^2 dt[/tex]

    Let:

    [tex]u=t^2[/tex]

    [tex]dv=e^{-st}dt[/tex]

    Really need to use parts for this. Also, this is a standard one that most ODE books will illustrate.
     
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