How can the Laplace transform of L[t^n] be proven?

  • Context: Undergrad 
  • Thread starter Thread starter mathwurkz
  • Start date Start date
  • Tags Tags
    Proof
Click For Summary

Discussion Overview

The discussion revolves around the proof of the Laplace transform of the function \( t^n \), specifically how it is derived and its relationship to the gamma function. The scope includes mathematical reasoning and technical explanation related to the Laplace transform.

Discussion Character

  • Technical explanation, Mathematical reasoning

Main Points Raised

  • One participant asks for clarification on how the Laplace transform \( L[t^n] = \frac{n!}{s^{n+1}} \) is derived, noting that they often see it in tables but do not understand its origin.
  • Another participant suggests performing the transformation and indicates that a change of variables can simplify the integral to relate it to the gamma function.
  • A third participant acknowledges the connection to the gamma function after receiving clarification.
  • A later reply provides a formal proof involving integration by parts, showing that the integral can be expressed in terms of the gamma function, ultimately leading to the result \( L[t^n] = \frac{n!}{s^{n+1}} \).

Areas of Agreement / Disagreement

Participants appear to agree on the relationship between the Laplace transform and the gamma function, but the discussion does not resolve all aspects of the proof process, as different methods are suggested.

Contextual Notes

The discussion includes assumptions about the properties of integrals and the gamma function, but these are not fully explored or resolved within the thread.

mathwurkz
Messages
41
Reaction score
0
Hey guys, how can this Laplace transform be proven. I always see it in the tables but don't know how it came to be.

[tex]L[t^n] = \frac{n!}{s^{n+1}}[/tex]
 
Physics news on Phys.org
Just do the transformation. With a simple change of variables you can reduce the integral to the gamma function.
 
Ah. Ok I got it thanks. I guess I must have let it slip by me that gamma function is related.
 
here is a formal proof:
You can show that
[tex]\int t^n e^{-ts} dt = -s^{-n-1}\int_{st}^{\infty}x^n e^{-x}dx +c[/tex]
therefore
[tex]\int_{0}^{\infty} t^n e^{-ts} dt =s^{-n-1}\int_{0}^{\infty}x^n e^{-x}dx =s^{-n-1} n![/tex]
 

Similar threads

  • · Replies 2 ·
Replies
2
Views
4K
  • · Replies 4 ·
Replies
4
Views
3K
  • · Replies 8 ·
Replies
8
Views
5K
  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 1 ·
Replies
1
Views
3K
  • · Replies 1 ·
Replies
1
Views
2K