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Please help me to solve this

  1. Dec 28, 2011 #1
    i just found this and try to solve.. but then since i left all of these for many years, so i cant remember some of the ways..

    i will keep thinking of this because i'm not able to solve it.. and this make me suffer..

    ∫ x / (1 + ex) dx


    please help me to solve this.. :)
     
  2. jcsd
  3. Dec 28, 2011 #2

    micromass

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    You can't solve this. This integral cannot be solved in terms of elementary functions. Specifically, you need the polylogarithm to solve this.
     
  4. Dec 28, 2011 #3
    ohh... i see... thank you micromass...
    but if you want to.. can you show how to solve this by using the polylogarithm? :)
     
  5. Dec 28, 2011 #4
    Do you have any background in complex analysis?
     
  6. Dec 28, 2011 #5
    yess.. but not so deep.. just a basic of complex analysis..
     
  7. Jan 1, 2012 #6
    this problem cannot be solved normally. you can use integration by parts

    integration by parts is this: ∫ u dv = u.v - ∫ v du
     
  8. Jan 1, 2012 #7

    HallsofIvy

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    What do you mean by that? "Integration by parts" is a normal integration method. And won't work here. As micromass said, that cannot be integrated in terms of elementary functions.
     
  9. Jan 2, 2012 #8
    If you know the polylogarithm functions, then the formal result is :
     

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