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Homework Help: Need a little help starting this integral

  1. Feb 12, 2006 #1
    [tex]\int\frac{1}{e^x+1}dx[/tex]

    I have tried substitution, partial fraction decomposition, and integration by parts but I cant seem to figure it out. Any help is much appriciated. o:)
     
  2. jcsd
  3. Feb 12, 2006 #2

    Physics Monkey

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    Hint: multiply top and bottom by [tex] e^{-x} [/tex].
     
  4. Feb 12, 2006 #3
    okay, then I can use u sub, which nets...

    [tex]-ln (1+e^{-x})[/tex]

    is that right?
     
    Last edited: Feb 12, 2006
  5. Feb 12, 2006 #4
    That does not seem right. What I have I done wrong?

    [tex]\int\frac{e^{-x}}{1+e^{-x}}dx[/tex]

    [tex]u = 1+e^{-x}\\-du = e^{-x}[/tex]

    [tex]-\int\frac{1}{u}du[/tex]
     
    Last edited: Feb 12, 2006
  6. Feb 12, 2006 #5
    It looks right to me, why do you think it's wrong?
     
  7. Feb 12, 2006 #6
    After further review, I dont think its wrong. I guess I am just working on building confidence in the integration process and I was hoping for some confirmation that is was done right. Thank you. These forums have been extremely helpful and I really appriciate all the quick and intelligent responces.
     
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