Please help me to solve this

  • Thread starter all-black
  • Start date
  • #1
13
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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.. :)
 

Answers and Replies

  • #2
22,129
3,297
You can't solve this. This integral cannot be solved in terms of elementary functions. Specifically, you need the polylogarithm to solve this.
 
  • #3
13
0
You can't solve this. This integral cannot be solved in terms of elementary functions. Specifically, you need the polylogarithm to solve this.

ohh... i see... thank you micromass...
but if you want to.. can you show how to solve this by using the polylogarithm? :)
 
  • #4
807
23
ohh... i see... thank you micromass...
but if you want to.. can you show how to solve this by using the polylogarithm? :)

Do you have any background in complex analysis?
 
  • #5
13
0
Do you have any background in complex analysis?

yess.. but not so deep.. just a basic of complex analysis..
 
  • #6
2
0
this problem cannot be solved normally. you can use integration by parts

integration by parts is this: ∫ u dv = u.v - ∫ v du
 
  • #7
HallsofIvy
Science Advisor
Homework Helper
41,847
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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.
 
  • #8
798
34
ohh... i see... thank you micromass...
but if you want to.. can you show how to solve this by using the polylogarithm? :)

If you know the polylogarithm functions, then the formal result is :
 

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