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Integration problem help

  1. Jan 19, 2008 #1
    1. The problem statement, all variables and given/known data
    what is the integral of (e^(-x)sin(x)) with limits 2 and 1


    2. Relevant equations



    3. The attempt at a solution

    let the integral be denoted as I
    i used integration by parts twice and i got that:
    I=[-e^(-x)(sin(x))] + [e^(-x)(sin(x))] + I

    i'm stuck now and dont know what to do, can someone help me please.
    thank you very much
     
  2. jcsd
  3. Jan 19, 2008 #2

    Dick

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    That's perfectly valid, but not very interesting. I think you used the wrong 'part' for one of your integrations by parts. In udv=d(uv)-vdu, you can use either the trig function or the exponential for v. In one integration you used the exponential and in the other the trig. Use the same one for both.
     
  4. Jan 19, 2008 #3
    Last edited: Jan 19, 2008
  5. Jan 19, 2008 #4

    arildno

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    First off, we get:
    [tex]I=-e^{-x}\sin(x)|^{x=2}_{x=1}+\int{e}^{-x}\cos(x)dx[/tex]
    Continue to use e^{-x} as u' in the integration by parts formula.
     
  6. Jan 19, 2008 #5
    thanx 2 all
    ;) ;) ;)
     
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