Convergence of an Integral with Increasing Exponent

In summary, the problem statement involves finding the limit of the integral of sin(pi*x^n) from x=0 to 1/2 as n approaches infinity. The attempt at a solution involves using Lebesgue's Dominated Convergence Theorem and u substitution, but it is determined that the limit does not exist due to sin(pi*x^n) not converging to a limit over the entire domain. However, it is clarified that the limit does not need to be considered for values outside of the given domain.
  • #1
abcd999
4
0

Homework Statement


[tex]lim n \rightarrow\inf \int sin(pi*x^{n})dx[/tex]
...integral is from x=0 to 1/2.


Homework Equations





The Attempt at a Solution


Lebesgue's Dominated Convergence Theorem says that I can move the limit inside, but only if fn converges pointwise to a limit f, which I don't believe it does. Even so, there is no limit as n approaches infinity of fn.
I also tried u substitution, setting u = pi*x^n, but that didn't get me anywhere.

Thanks in advance
 
Physics news on Phys.org
  • #2
Doesn't x^n converge to zero for x in [0,1/2]? Or am I confused?
 
  • #3
It does, but in order to move the limit inside and use Lebesgue's, doesn't sin(pi*x^n) have to converge to a limit over the entire domain, not just [0,1/2]?
 
  • #4
Not as far as I know. You are only integrating over [0,1/2]. Why do you have to worry about values outside of that range? Just call the domain [0,1/2].
 
  • #5
I guess I was over thinking it. Thanks for your help.
 

1. What is the definition of the limit of an integral?

The limit of an integral is the value that the integral approaches as the interval over which it is evaluated becomes infinitely small. It represents the exact value of the integral at a given point on the function.

2. How is the limit of an integral calculated?

The limit of an integral is calculated by first evaluating the integral over a small interval and then taking the limit as the interval size approaches 0. This can be done using various methods such as Riemann sums, the Fundamental Theorem of Calculus, or the Mean Value Theorem.

3. What is the significance of the limit of an integral in calculus?

The limit of an integral is a fundamental concept in calculus as it allows for the calculation of exact areas under curves and the determination of important properties of functions such as continuity and differentiability. It is also used in many real-world applications such as finding the total distance traveled by an object given its velocity function.

4. Can the limit of an integral be evaluated at any point on the function?

No, the limit of an integral can only be evaluated at points where the function is continuous. This is because the limit of an integral relies on the concept of a limit, which only exists for continuous functions.

5. How does the limit of an integral relate to the concept of a derivative?

The limit of an integral is closely related to the concept of a derivative through the Fundamental Theorem of Calculus. The derivative of a function is equal to the limit of the integral of the function over a small interval as the interval size approaches 0. This allows for the calculation of derivatives without having to use the limit definition directly.

Similar threads

  • Calculus and Beyond Homework Help
Replies
3
Views
401
  • Calculus and Beyond Homework Help
Replies
5
Views
1K
  • Calculus and Beyond Homework Help
Replies
12
Views
1K
  • Calculus and Beyond Homework Help
Replies
2
Views
830
  • Calculus and Beyond Homework Help
Replies
15
Views
775
  • Calculus and Beyond Homework Help
Replies
3
Views
639
  • Calculus and Beyond Homework Help
2
Replies
47
Views
2K
  • Calculus and Beyond Homework Help
Replies
11
Views
1K
  • Calculus and Beyond Homework Help
Replies
22
Views
1K
  • Calculus and Beyond Homework Help
Replies
3
Views
262
Back
Top