1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Inverse Laplace help

  1. Dec 2, 2016 #1
    1. The problem statement, all variables and given/known data
    [tex] F(s) = \frac{s^2e^{-4s}}{s^2+9}[/tex]

    2. Relevant equations
    [tex] \mathcal{L} ({f(t-a)\mathcal{H}(t-a)}) = e^{-as}F(s) [/tex]

    3. The attempt at a solution

    [tex] F(s) = e^{-4s}(\frac{s^2}{s^2+9}) [/tex]
    using [tex] \mathcal{L} {f(t-a)\mathcal{H}(t-a)} = e^{-as}F(s) [/tex]
    [tex] f(t) = cos(3t-12)\mathcal{H}(t-4) [/tex]

    I do not understand why this is incorrect. My professor got [tex]f(t) = \delta(t - 4) - 3sin(3t - 12)\mathcal{H}(t-4) [/tex]

    EDIT: Wow I get it now, it's because [tex] \mathcal{L}(cos(kt)) = \frac{s}{s^2+k} [/tex] not [tex]\mathcal{L}(cos(kt)) = \frac{s^2}{s^2+k} [/tex] stupid mistake lol
     
    Last edited: Dec 2, 2016
  2. jcsd
  3. Dec 8, 2016 #2
    Thanks for the thread! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post? The more details the better.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Inverse Laplace help
  1. Inverse Laplace Help (Replies: 5)

Loading...