1. Dec 28, 2011

### all-black

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

2. Dec 28, 2011

### micromass

Staff Emeritus
You can't solve this. This integral cannot be solved in terms of elementary functions. Specifically, you need the polylogarithm to solve this.

3. Dec 28, 2011

### all-black

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

4. Dec 28, 2011

### Number Nine

Do you have any background in complex analysis?

5. Dec 28, 2011

### all-black

yess.. but not so deep.. just a basic of complex analysis..

6. Jan 1, 2012

### vishalhd

this problem cannot be solved normally. you can use integration by parts

integration by parts is this: ∫ u dv = u.v - ∫ v du

7. Jan 1, 2012

### HallsofIvy

Staff Emeritus
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. Jan 2, 2012

### JJacquelin

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

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