How to Prove the Laplace Transform of f(t/b) Equals bF(bs) for b ≠ 0?

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Homework Help Overview

The discussion revolves around proving the relationship between the Laplace transform of a function scaled by a constant factor and the Laplace transform of the original function. Specifically, the original poster seeks to demonstrate that L{f(t/b)} = bF(bs) for b ≠ 0, focusing on the transformation of the variable within the integral.

Discussion Character

  • Exploratory, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the use of a substitution method to change the integration variable from t to u, specifically suggesting u = t/b. There are questions about how to correctly adjust the exponential term in the Laplace transform and whether additional factors are needed when changing the differential from dt to du.

Discussion Status

Participants are actively engaging with the problem, exploring substitution techniques and the implications of changing variables in the context of the Laplace transform. Guidance has been provided regarding the necessary adjustments to the exponential term and the differential, indicating a productive direction in the discussion.

Contextual Notes

There is an emphasis on ensuring that the transformations adhere to the rules of calculus, particularly concerning the handling of differentials during substitution. The original poster has not yet provided a complete solution, and the discussion remains focused on the steps involved in the proof.

magnifik
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show that L{f(t/b)} = bF(bs), b is not equal to 0

i know that
L{f(t)} = \inte-stf(t) dt = F(s)
so
L{f(t/b)} = \inte-stf(t/b) dt

any tips on how to start? thx
 
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Do a u substitution to change the integration variable. Substitute u=t/b.
 
do i also have to plug in (t/b) into e-st so that it becomes e-s(t/b) ?
 
magnifik said:
do i also have to plug in (t/b) into e-st so that it becomes e-s(t/b) ?

You need to write e^(-st) in terms of u.
 
so..
u = t/b
t = bu
e^(-st)
e^(-sbu)
 
magnifik said:
so..
u = t/b
t = bu
e^(-st)
e^(-sbu)

Sure. Now don't forget to add a factor to change the dt to a du.
 

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