Indefinite Integral for -.5*(ln(2))^2

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Discussion Overview

The discussion revolves around evaluating the integral of ln(x)/(e^x+1) from 0 to infinity. Participants explore various methods for solving this integral, including differentiation under the integral sign and contour integration, while sharing their experiences with different approaches.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested, Mathematical reasoning

Main Points Raised

  • One participant expresses a desire for a simpler method to evaluate the integral from 0 to infinity of ln(x)/(e^x+1).
  • Another participant suggests using differentiation under the integral sign and contour integration as potential methods, though they have not tried them.
  • There is a request for clarification regarding the form of the denominator, with one participant confirming it is (e^x)+1.
  • A participant shares their unsuccessful attempts using limits, integration by parts, and a limit involving the Dirichlet eta function, indicating the complexity of the limit they encountered.
  • The limit mentioned is lim x->+1 (\Gamma(x)\eta(x)-ln(2))/(x-1), with a request for any helpful tricks related to it.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus on the best method to evaluate the integral, and multiple competing approaches are discussed without resolution.

Contextual Notes

Some methods mentioned may depend on specific assumptions or definitions, and the complexity of the limit involving the Dirichlet eta function remains unresolved.

SumThePrimes
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Hello, I have recently encountered an integral that I have been able to evaluate in a sick, unholy way, and for making a proof much more elegant I would like a simple way to evaluate the integral from 0 to infinity of ln(x)/(e^x+1) . thank you!
 
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I haven't tried them but maybe differentiation under the integral sign (set 1 to any arbitrary number) and contour integration?
 
Is the denominator you have listed e^(x+1) or (e^x)+1? Just want to verify before trying the problem.
 
flyintiger said:
Is the denominator you have listed e^(x+1) or (e^x)+1? Just want to verify before trying the problem.

It is (e^x)+1 . I tried using limits on the bounds and then integration by parts and then switching certain values to other limited integrals and canceling... I tell you what that didn't work. I also tried a limit for the natural logarithm with an integral for the Dirichlet eta function, but that gave me a very tough looking limit that I had no chance with.

edit: The limit was lim x->+1 (\Gamma(x)\eta(x)-ln(2))/(x-1) , if anyone has some cool trick for that.
 
Last edited:

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