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Intergration by parts

  1. Feb 19, 2009 #1
    1. The problem statement, all variables and given/known data
    solve by using intergration by parts x^2(cosx)dx

    2. Relevant equations
    My question is i got this answer but my computer algebra system gave me this answer
    (x^2-2)sin(x)+2xcos(x) can you tell me where i went wrong??

    3. The attempt at a solution
    u=X^2
    dv=cosx
    du=dx
    v=sinx

    Sx^2(cosx)dx=uv-Svdu=x^2(sinx)-Ssinxdx

    S2xcosxdx=2xsinx-(-cosx)+c= final answer= 2xsinx+cosx+C
     
  2. jcsd
  3. Feb 19, 2009 #2

    Dick

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    Science Advisor
    Homework Helper

    If u=x^2, du=2x*dx. Not du=dx. You have to do integration by parts twice. And why are you integrating 2xcos(x)?
     
  4. Feb 19, 2009 #3
    oo thank you
     
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