Improper Integrals, Infinite Limits

In summary, the integral of e^-Sxsin(ax) with limits from 0 to infinity, where S and A are constants, can be simplified to -(S^2)/S(S^2+a^2). This is due to the fact that sin(ax) is bounded by -1 and 1, and the limit of e^-x as x approaches infinity is 0. The final solution is obtained by taking the limit c→∞ in the integrand.
  • #1
Magnawolf
25
0

Homework Statement



∫e-Sxsin(ax) dx, S and A are constants, upper limit is ∞ lower is 0

Homework Equations



∫ u dv = uv - ∫ vdu

The Attempt at a Solution



After integrating by parts twice I got:

(S2)/S(S2+a2) lim c→∞ [-sin(ax)e-Sx + acos(ax)e-Sx] |[itex]^{C}_{0}[/itex]

Okay, now how on Earth do I take the lim c→∞ if sin(ax) is periodic? Since limx→∞ e^-x=0 would it just be (S2)/S(S2+a2) [(0+0) - (0+1)] which becomes
-(S2)/S(S2+a2)?
 
Last edited:
Physics news on Phys.org
  • #2
Magnawolf said:

Homework Statement



∫e-Sxsin(ax) dx, S and A are constants, upper limit is ∞ lower is 0

Homework Equations



∫ u dv = uv - ∫ vdu

The Attempt at a Solution



After integrating by parts twice I got:

(S2)/S(S2+a2) lim c→∞ [-sin(ax)e-Sx + acos(ax)e-Sx] |[itex]^{C}_{0}[/itex]

Okay, now how on Earth do I take the lim c→∞ if sin(ax) is periodic?
sin(ax) is bounded.

-1 ≤ sin(ax) ≤ 1
 
  • #3
Yeah I know but how do you take the limit of something that's bounded by two numbers? I'm assuming you can't. What I got was that since limx→∞ e^-x=0 would it just be (S2)/S(S2+a2) [(0+0) - (0+1)]? which becomes -(S2)/S(S2+a2). I just want to verify that this is the answer.
 

Related to Improper Integrals, Infinite Limits

1. What is an improper integral?

An improper integral is an integral that cannot be evaluated using the standard methods of integration. It occurs when one or both of the limits of integration are infinite or when the function being integrated is not defined at certain points within the interval of integration.

2. How do you determine if an improper integral converges or diverges?

To determine if an improper integral converges or diverges, you must evaluate the integral using a limit. If the limit exists and is a finite number, then the integral converges. If the limit does not exist or is infinite, then the integral diverges.

3. Can an improper integral have a finite value even if one or both of the limits of integration are infinite?

Yes, an improper integral can have a finite value even if one or both of the limits of integration are infinite. This can occur if the function being integrated approaches zero faster than the limits approach infinity.

4. What are the different types of improper integrals?

The two types of improper integrals are Type 1 and Type 2. Type 1 improper integrals have one or both limits of integration as infinity, while Type 2 improper integrals have a discontinuity or infinite value within the interval of integration.

5. How do you evaluate an improper integral?

To evaluate an improper integral, you must first determine if it converges or diverges. If it converges, you can use a limit to evaluate the integral. If it diverges, you can use a comparison test, limit comparison test, or the Cauchy condensation test to determine the behavior of the integral.

Similar threads

  • Calculus and Beyond Homework Help
Replies
2
Views
332
  • Calculus and Beyond Homework Help
Replies
8
Views
1K
  • Calculus and Beyond Homework Help
Replies
3
Views
2K
  • Calculus and Beyond Homework Help
Replies
13
Views
2K
  • Calculus and Beyond Homework Help
Replies
5
Views
1K
  • Calculus and Beyond Homework Help
Replies
10
Views
1K
  • Calculus and Beyond Homework Help
Replies
4
Views
827
Replies
2
Views
1K
Replies
9
Views
1K
  • Calculus and Beyond Homework Help
Replies
22
Views
2K
Back
Top