Which method should I use for integrating (x^2+x)^-1?

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Discussion Overview

The discussion revolves around methods for integrating the function \((x^2+x)^{-1}\). Participants explore various techniques including integration by parts, completing the square, trigonometric substitution, and partial fractions. The scope includes theoretical approaches and practical application of integration techniques.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant suggests using integration by parts after separating the integral into \(\int \frac{1}{x} \frac{1}{x+1}dx\) but is uncertain about the choice of \(u\).
  • Another participant proposes completing the square and using trigonometric substitution, providing a specific transformation of the integrand.
  • A different participant advocates for the method of partial fractions, presenting the decomposition \(\frac{1}{x(x+1)} = \frac{1}{x} - \frac{1}{x+1}\).
  • One participant references a solution found via Wolfram Alpha that involved hyperbolic functions, expressing some intimidation by that approach.
  • Another participant notes that partial fractions is a standard method typically introduced in earlier algebra courses, highlighting its current placement in calculus and differential equations curricula.
  • A suggestion is made to compare results from different methods, indicating that one approach yields an expression for arctanh in terms of the natural logarithm.

Areas of Agreement / Disagreement

Participants present multiple competing methods for integration, with no consensus on a single preferred approach. The discussion remains unresolved regarding which method is best.

Contextual Notes

Some methods proposed may depend on specific assumptions about the integrand or the familiarity of participants with certain techniques. The discussion does not resolve the appropriateness of each method for this particular integral.

TylerH
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I'm learning integration by parts, and thought this would be a good test of my understanding.

I've separated it into something that seems better.
[tex]\int \frac{1}{x^2+x}dx = \int \frac{1}{x} \frac{1}{x+1}dx[/tex]

I'm guessing I use integration by parts from here, but which should I make u?
 
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Have you thought about completing the square and then using a trigonometric substitution:

ie x^2 + x + 1/4 - 1/4 = (x + 1/2)^2 - (1/2)^2
 
Partial fractions would be a good approach.

[tex]{1\over x(x+1)} = {1\over x} - {1\over x+1}[/tex]
 
chiro: That was how Wolfram Alpha did it. It was the hyperbolic tangent that scared me away. :)

PhDorBust: That's awesome. Directly to the solution, too. Could you explain how you spotted that?
 
^Partial fractions is a standard method that used to be learned in elementary algebra. Now it has been pushed into elementary calculus elementary ordinary differential equations or e, usually in chapters with names like "more integrals yay!" and "Laplace transforms woo!" respectively.
 
And I thought I hated U substitution...
 
Well, I suggest you do the integral through both methods and compare the results. You'll get an expression for the arctanh in terms of the natural logarithm function which is somewhat expected, since the tanh is defined in terms of the exponential in base <e>.
 

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