Solving Difficult Integrals: Any Ideas for This Tricky Integral?

  • Context: Graduate 
  • Thread starter Thread starter Schrodinger's Dog
  • Start date Start date
  • Tags Tags
    Integral
Click For Summary

Discussion Overview

The thread discusses various challenging integrals, specifically focusing on the integral of a function involving an exponential and a power of x, as well as the integral of the square root of sine cubed. Participants explore potential methods for solving these integrals, including substitutions and integration by parts, while expressing uncertainty about the solvability in elementary functions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant presents the integral \(\int \frac{3}{2}x^{-\frac{1}{2}}\cdot e^{\frac{3}{2}x^{-2}}\,dx\) and questions its solvability beyond using a Taylor series.
  • Another suggests a substitution \(u = \sqrt{x}\), which simplifies the integral to one involving \(e^{u^{-4}}\).
  • Concerns are raised about discrepancies in results from different computational tools, with one participant noting that Mathematica indicates the integral is unsolvable.
  • Further discussion includes attempts to clarify the expression of the integral and the results obtained from Mathematica, with one participant mentioning a gamma function as part of the solution.
  • A separate integral involving \(\int \sin^{\frac{3}{2}}(x)\;dx\) is introduced, with participants expressing uncertainty about its solvability and discussing potential substitutions.
  • One participant claims to have derived an expression for the integral in terms of elementary functions using integration by parts and substitution.
  • Another participant expresses admiration for the approach taken and seeks clarification on the substitution method used.
  • There is a discussion about the creativity involved in solving integrals and the subjective nature of finding effective substitutions.

Areas of Agreement / Disagreement

Participants express differing views on the solvability of the integrals discussed, with some suggesting methods that may lead to solutions while others remain skeptical about the existence of elementary solutions. The discussion remains unresolved regarding the integrals' solvability.

Contextual Notes

Some participants mention limitations in their computational tools and the potential for errors in inputting expressions, which may affect the results obtained. The discussion also highlights the complexity of the integrals and the various approaches that may or may not yield satisfactory results.

  • #31
Ok I'm sure everyone is bored to death by this by now, but I'm finding it quite interesting and quite informative for someone who's forget a lot about integration, so with that in mind it might be of use to someone, here's how he justifies the a in the integral and calling it "definite".

(2)... The point about the constants is an important one. If, for example, you have I = e^{ax}dx, then you can effectively get rid of the constant, a, from being inside the integral, by simply substituting for, say, t = ax. Differentiating this, we get dt = a dx. Rearranging, therefore dx = dt/a. Substitute in the integral, for ax, and dx, and we now get,
I = (e^{t}dt)/a .We divide I by the factor a, but a has now come outside the integral of (e^{t}dt) .

(3)... We can do a similar substitution for pretty well any integral.So in general, if I = f(ax)dx, where f is some function, then I=(f(t)dt)/a .

I can't see a problem with this, but then I'm seriously not that good, or that au fait atm with it all, although it's coming back gradually.
 

Similar threads

  • · Replies 4 ·
Replies
4
Views
3K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 31 ·
2
Replies
31
Views
4K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 6 ·
Replies
6
Views
3K
  • · Replies 4 ·
Replies
4
Views
1K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 16 ·
Replies
16
Views
4K