Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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

    User Avatar
    Science Advisor
    Homework Helper

    [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.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook




Loading...
Similar Threads for Need help compute
I Need a help in solving an equation (probably differentiation