Integral - an alternative to expanding the denominator?

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Discussion Overview

The discussion revolves around the integral \(\int\frac{1}{(x+1)^7-x^7-1}dx\) and explores alternative methods for solving it, particularly whether there are approaches other than expanding the denominator. Participants express varying opinions on the complexity of the integral and the methods proposed.

Discussion Character

  • Exploratory
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants suggest using integration by substitution, though they express concerns about potential complications arising from this method.
  • One participant describes the integral as "horrible" and questions the claim that it can be easily solved by expansion, seeking clarification on the proposed solution.
  • Another participant applies the binomial theorem to expand the denominator and provides a factorization, indicating that partial fraction decomposition could lead to a solution.
  • There is a discussion about the difficulty of factorizing the polynomial and the complexity involved in performing partial fraction decomposition, with one participant expressing that the process is lengthy and annoying.
  • Some participants challenge the characterization of the integral as "easy," with differing views on the time required to compute it versus the time taken to type out the solution.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the ease of solving the integral. There are competing views on the complexity of the methods discussed, with some asserting that the integral is difficult while others suggest it is manageable.

Contextual Notes

The discussion highlights the assumptions involved in factorization and the subjective nature of what constitutes an "easy" solution, as well as the potential for varying interpretations of the integral's complexity.

LikeMath
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Integral -- an alternative to expanding the denominator?

The following integral can be easily solved by expanding the denominator but I am wondering if there is a another way to solve it

\int\frac{1}{(x+1)^7-x^7-1}dx
 
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You could try doing integration by substitution, and then repeating it several (probably 7) times. But I'm sure you would either end up with something really ugly or encounter a problem pretty early on that stops you.
 


LikeMath said:
The following integral can be easily solved by expanding the denominator but I am wondering if there is a another way to solve it

\int\frac{1}{(x+1)^7-x^7-1}dx



Would you be so kind as to show us how this integral is "easily" solved expanding whatever? I think this is a rather

horrible integral, expanding or not, and more than finding a way to make it more or less normal I'd love to see what's your way to solve it.

Thanx

DonAntonio
 


DonAntonio said:
Would you be so kind as to show us how this integral is "easily" solved expanding whatever? I think this is a rather

horrible integral, expanding or not, and more than finding a way to make it more or less normal I'd love to see what's your way to solve it.

Thanx

DonAntonio

By the binomial theorem we get
(x+1)^7-x^7-1=7(x^6+3x^5+5x^4+3x^2+x)
now if we factorize this term we also get
x(x+1)(x^2+x+1)^2
then partial fraction completes the solution.
 


LikeMath said:
By the binomial theorem we get
(x+1)^7-x^7-1=7(x^6+3x^5+5x^4+3x^2+x)
now if we factorize this term we also get
x(x+1)(x^2+x+1)^2
then partial fraction completes the solution.


Well, yes...but for this you must first (1) know how to factorize the polynomial (a quintic, since zero is obvious), perhaps by "guessing

that -1 is a root, and (2) you must still make the partial fractions stuff, which seems far from being that easy, as \frac{1}{x(x+1)(x^2+x+1)^2}=\frac{A}{x}+\frac{B}{x+1}+\frac{Cx+D}{x^2+x+1}+\frac{Ex+F}{(x^2+x+1)^2}
A matter of taste, I guess...perhaps because I'm a theoretical mathematician I wouldn't dare call the above "easy", or perhaps I would

but I'd add immediately "annoying and long" after that.

DonAntonio
 


Yes you are right, "easy" was not appropriate.
 


Hi !
Who said "it's not easy" ?
It takes less time to compute it that to type it. :redface:
 

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JJacquelin said:
Hi !
Who said "it's not easy" ?
It takes less time to compute it that to type it. :redface:



Really...?! Common, it's nice to show off but not with this petty things.

DonAntonio
 

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