Why is substituting for \int\frac{dx}{x^4+1} so difficult?

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    Integral Substitution
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Discussion Overview

The discussion revolves around the challenges of evaluating the integral \(\int\frac{dx}{x^4+1}\). Participants explore various substitution methods, including trigonometric and hyperbolic substitutions, as well as the use of partial fractions, while expressing frustration over the complexity of the integral.

Discussion Character

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

Main Points Raised

  • One participant recalls a previous experience with a substitution like \(x=e^u\) but finds no substitution effective for this integral.
  • Another suggests that using the substitution could lead to a hyperbolic trigonometric function, although they do not assert this will work.
  • A third participant presents a complex expression they claim is the result of the integral, though its correctness is not established.
  • One participant proposes factoring the denominator as a potential method to simplify the integral.
  • Another participant questions whether the integral could simply be \(\ln|x^4+1|\), but this claim is challenged by others.
  • There is a discussion about the necessity of having a complete differential \(du\) in substitution, which is noted to be absent in the current context.
  • One participant raises a point about the integral of \(1/x^2\) and its relation to logarithmic functions, but this is met with skepticism regarding its relevance.

Areas of Agreement / Disagreement

Participants express differing opinions on the methods to tackle the integral, with no consensus reached on a definitive approach or solution. The discussion remains unresolved with multiple competing views presented.

Contextual Notes

Some participants' claims depend on specific assumptions about substitution techniques and the structure of the integral, which are not universally accepted within the discussion.

Jupiter
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[tex]\int\frac{dx}{x^4+1}[/tex]
What really frustrates me is that I've seen this integral before. I believe it involved some whacky subsitution like [tex]x=e^u[/tex], but no substitution seems to work. Partial fractions just make a mess. Trig subs seem tempting but that 4 screws everything up. Ideas?
 
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If you do that whacky substitution, how about then multiplying through to get e^(2u)+e^(-2u) and getting a hyperbolic trig function? Not saying this works.
 
[tex]\int\frac{dx}{x^4+1}=\frac{1}{3\sqrt{2}}<br /> \left(2\arctan(1+\sqrt{2}x)-2\arctan(1-\sqrt{2}x)+\right.[/tex]

[tex]\left.\log(\sqrt{2}x+x^2+1)-\log(\sqrt{2}x-x^2-1)\right)[/tex]
 
You could factor the denominator!
 
isn't the integral of 1/x^4+1 just the ln|x^4+1|? or something like that?
 
No, differentiate log(x^4+1) and you'll see why.
 
noooo. i mean, the integral of 1/u is the ln|u|+c and in this case, 1/u = (x^4+1)
 
In order to do that, you also need to have a full [itex]du[/itex] on your integrand, which would need an [itex]x^3[/itex] term that is not there.
 
Also not that if you're correct that the integral of 1/x^2 is log(x^2) and, obviously -1/x as well, so up to a constant 2logx = -1/x?
 

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