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Laplace differentiation question

  1. Jun 14, 2009 #1
    Hi i'm learning laplace transform, specifically multiplying by 't' and 't^n'. Now i understand the concept that L{tf(t)} = -F'(s) but i'm confused with the differentiation part of the process (having a bit of a dim moment!).

    Here is the example it gives:

    L{sin2t} = 2 / (s^2 + 4), therefore L{tsin2t} = -d/ds(2 / (s^2 +4)) = 4s / (s^2 + 4)^2

    the differentiation at the end is the bit that is confusing me i.e. how to do it. I know this should be the simple bit but it completely evades my understanding at this point :rofl:.

    Any help would be appreciated

  2. jcsd
  3. Jun 14, 2009 #2


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    Science Advisor

    I'll assume you know how to differentiate. Let u=s2+4.
    d/ds(2/u)=-(2/u2)du/ds. du/ds=2s. Just put it all together.
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