Integrating a quadratic funtion raised to m/n

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    Integrating Quadratic
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Discussion Overview

The discussion revolves around the integration of a quadratic function raised to a fractional power, specifically in the form \(\int (a x^{2}+ bx +c) ^{\frac{m}{n}}dx\), with limits from -∞ to +∞. Participants explore convergence issues, substitution methods, and reference integral tables to find solutions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning
  • Homework-related

Main Points Raised

  • One participant questions the convergence of the integral, noting that the function does not approach zero as \(x\) approaches ±∞.
  • Another participant shares a specific integral from a physics problem, seeking assistance in solving \(\int(z^{2} -8z + 36)^\frac{-3}{2} dz\) over the same limits.
  • A suggestion is made to consult integral tables, with a reference to a specific integral that may help in finding a solution.
  • Participants discuss the use of substitutions to simplify the integrand, with one proposing to rewrite the quadratic expression in a different form to facilitate integration.
  • There is a challenge regarding the substitution method, as one participant expresses confusion about the presence of \(z\) in the denominator after substitution.
  • Another participant provides a clearer substitution pathway, suggesting a transformation that simplifies the integral further.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the convergence of the integral, and there are multiple approaches suggested for solving the integral, indicating that the discussion remains unresolved.

Contextual Notes

Some participants express uncertainty about the convergence of the integrals and the effectiveness of their proposed substitution methods, highlighting the complexity of the problem.

Who May Find This Useful

Readers interested in advanced integration techniques, particularly those involving quadratic functions and fractional powers, may find this discussion beneficial.

mdnazmulh
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I couldn't figure out what to do with this type of integration [tex]\int (a x^{2}+ bx +c) ^{\frac{m}{n}}dx[/tex] here m, n are integer numbers. Integration limit -∞ to +∞.
Will Binomial expansion work?
Please give me some clue.
 
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What makes you think that these integrals converge? The function to be integrated does not even converge to zero as x-> +/- infinity...!
 
Actually I had to solve an integral [tex]\int(z^{2} -8z + 36)^\frac{-3}{2} dz[/tex] limit - infinity to + infinity in a physics problem. dz is the differential length of a conducting wire extending from -infinity to + infinity.
Can you please help me how can I solve above integral?
 
Well, the easiest way is probably to look it up it an table of integrals:smile:

Wikipedia states that
826cfb9c30857b16d144b1b5b4c7cc04.png


where s is the square root of x^2-a^2...taking m=0, n=1 should help you.maybe that is not the bsst way to go.

I rather suggest the following; use simple substitutions to reduce the integrand to
[tex] (x^2+1)^{-3/2}[/tex]

then use [itex]x=\sinh(z)[/itex] to obtain
[tex] \int_{\mathbb{R}}{\frac{dz}{\cosh(z)^2}}[/tex]

Once you have that, we can think about the next steps:smile:
 
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you gave me a good idea to look it up in integral table. I found one http://www.integral-table.com/

I found quite similar integral in no. 40 in the table's list ( sorry it's quite difficult to write that integral along with its result here) . But How can I obtain that result?
 
have you simplified your integral to something which looks similar to
[tex] \int_{\mathbb{R}}{\frac{dz}{\cosh(z)^2}}[/tex]

?
 
I'm puzzled at the substitution method u suggested. 1st would I let,
z^2- 8 z + 36 = u
2z -8 =du/dz
but dz = du/ (2z-8)
see there's a 'z' in the denominator on right hand side. So, letting z^2- 8 z + 36 = u won't work. What I can do now?
 
Well...x^2-8x+36 = (x-4)^2+20

thus your first substitution would be

y = x-4.

then

w = y/sqrt(20)

and finally

sinh(z)= w.
 
yeah. Thank u so much . Now I think I can manage the rest of the things.
 

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