Solving a Nasty Integral: Any Ideas?

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Discussion Overview

The discussion revolves around the integral \(\int\sqrt{[1-sech(u)]^{2}+ [-tanh(u)sech(u)]^{2}}du\). Participants explore various approaches to solve this integral, considering substitutions and potential transformations, while grappling with its complexity.

Discussion Character

  • Exploratory
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant suggests that the presence of sech(u) and its derivative -tanh(u)sech(u) indicates a possible substitution, but expresses concern about the complexity introduced by the radical.
  • Another participant questions the assumption that a primitive function can be expressed in terms of simple functions, implying skepticism about the integral's solvability.
  • A different participant proposes using the generalized binomial expansion, suggesting that this might lead to a hypergeometric solution.
  • One contributor offers a transformation involving trigonometric identities, attempting to simplify the expression, but acknowledges uncertainty about the correctness of their approach.
  • Several participants clarify that sech(x) refers to the hyperbolic secant function, not the secant of a function H(x), correcting a misunderstanding in the discussion.

Areas of Agreement / Disagreement

Participants express differing views on the solvability of the integral and the methods to approach it. There is no consensus on a specific solution or method, and the discussion remains unresolved.

Contextual Notes

Some assumptions about the functions involved and their properties may be missing, and the discussion reflects uncertainty regarding the applicability of certain mathematical transformations.

WalkingInMud
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Any Ideas on how to Approach this one? ...

\int\sqrt{[1-sech(u)]^{2}+ [-tanh(u)sech(u)]^{2}}du

We have a sech(u) and its derivative -tanh(u)sech(u) and this suggests some sort of substitution maybe, but the radical makes it a bit nasty for Me.

Any Ideas? ...Thanks Heaps,
 
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Why would you think there exists a primitive which can be expressed as a combinaton of "simple" function?
 
I doubt this will have a pretty substitution
Maybe use the generalized binomial expansion...

If that works you'll probably get a hypergeometric solution.
 
Hello there

I am not sure but I have few ideas and they might help.

[1-secH(X)]^2 becomes -tanH(X)

[cosX]^2 + [SinX]^2 = 1

Dvide by [cosX]^2 and you will have

1+[TanX]^2 = 1 over CosX^2 which [SecX]^2
1- [SecX]^2 = -[tanX]^2

The root of the first one is -[tanX] if I am not mistaken.
The Second one becomes [-SecH(x)]^2

This works if H is not a constant.
 

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