Appropriate Change of Variables for integration

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Discussion Overview

The discussion focuses on finding an appropriate change of variables for the integral \(\int_{-\infty}^{\infty}\frac{dt}{(a^2+t^2)^{3/2}}\). Participants explore various substitution methods and approaches related to integration techniques, including trigonometric and hyperbolic functions.

Discussion Character

  • Exploratory
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant seeks hints for a suitable change of variables for the integral.
  • Another participant confirms a transformation leading to \(\frac{2}{a^2} * \int_{0}^{\frac{\pi}{2}} \cos{t}dt\) and suggests a \(\tan^{-1}\) substitution.
  • A different participant questions whether the same change of variable applies as for \(\int \frac{dx}{a^2 + x^2}\) or \(\int \sqrt{a^2 + x^2} \, dx\).
  • One participant advocates for using hyperbolic trigonometric functions, suggesting \(\sinh x\) as a substitution.
  • Another participant presents an expression involving a table of integrals and algebra but expresses uncertainty about its validity.
  • A participant questions the manipulation of the integral involving the square of \(t\) and seeks clarification on the substitution's application.

Areas of Agreement / Disagreement

Participants express differing views on the appropriate substitution methods, with no consensus on a single approach. Some support trigonometric substitutions, while others suggest hyperbolic functions or question the validity of presented manipulations.

Contextual Notes

Participants reference various integral forms and substitution techniques, but there are unresolved mathematical steps and assumptions regarding the validity of the transformations used.

Flyboy27
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Can anyone give me any hints as to find a suitable change of variables for this integral.

infinity
/
|dt/(a^2+t^2)^3/2 =
|
/ -infinity


=2/a^2 * integral below
Pi/2
/
| cos t dt
|
/ 0


Thank you in advance
 
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[tex]\int_{-\infty}^{\infty}\frac{dt}{(a^2+t^2)^\frac{3}{2}} = \frac{2}{a^2} *<br /> \int_{0}^{\frac{\pi}{2}} \cos{t}dt[/tex]

Is this correct?

I think you can do a [itex]\tan^{-1}[/itex] substitution and use triangles to rewrite the integral.
 
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Shouldn't it be the same change of variable as for

[tex] \int \frac{dx}{a^2 + x^2}[/tex]

or

[tex] \int \sqrt{a^2 + x^2} \, dx[/tex]

?
 
I've always supported hyperbolic trig.functions used in substitutions.In your case,it's ~[tex]\sinh x[/tex]...

Daniel.
 
Alright using a table of integrals and some algebra here is what I have so far:

[tex]\int_{-\infty}^{\infty}\frac{dt}{(a^2+t^2)^\frac{3}{2}} = <br /> <br /> \int_{-\infty}^{\infty}\frac{a}{t^2(a^2+t^2)^\frac{3}{2}} + \frac{3}{t^2}}\int_{-\infty}^{\infty}\frac{dt}{(a^2+t^2)^\frac{1}{2}}[/tex]


Am I getting anywhere...I don't think so...
 
How did u pull that square 't' outta the integral...?:eek:

Daniel.
 
I used a table of integrals...and some simple algebra, unless I looked at the wrong intergral form, but I don't think I did, so anyway, where do I use the substitution?
 

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