Laplace & Inverse Laplace transforms

Click For Summary
SUMMARY

The discussion centers on solving differential equations using Laplace transforms, specifically addressing the accuracy of solutions derived through partial fraction decomposition. The user attempted to solve an equation but encountered discrepancies in their work, particularly in the factorization of polynomials. Key errors identified include the incorrect assertion that \(s^2 + 9\) factors as \((s - 3)(s + 3)\) and the misfactorization of \(s^2 + 6s + 8\). These mistakes highlight the importance of correct polynomial factorization in Laplace transform applications.

PREREQUISITES
  • Understanding of Laplace transforms and their applications in solving differential equations.
  • Knowledge of polynomial factorization techniques.
  • Familiarity with partial fraction decomposition in the context of Laplace transforms.
  • Basic concepts of stability in control systems, particularly regarding poles in the right-hand plane.
NEXT STEPS
  • Study the properties and applications of Laplace transforms in solving linear differential equations.
  • Learn advanced polynomial factorization techniques to avoid common mistakes.
  • Explore the implications of pole locations in the right-hand plane on system stability.
  • Review examples of partial fraction decomposition specifically tailored for Laplace transforms.
USEFUL FOR

Students studying differential equations, engineers applying Laplace transforms in control systems, and anyone seeking to improve their understanding of polynomial factorization in mathematical contexts.

Cocoleia
Messages
293
Reaction score
4

Homework Statement


I am given this equation:
upload_2018-1-18_16-39-58.png

and asked to solve using Laplace transforms

The Attempt at a Solution


This is what I did:
upload_2018-1-18_16-41-29.png

upload_2018-1-18_16-41-56.png

This seemed logical to me, I used partial fractions and it stayed pretty simple.

This is what the solutions my prof posted do:
upload_2018-1-18_16-42-33.png


Is my answer equivalent to this, or are their faults in my logic and work ?
 

Attachments

  • upload_2018-1-18_16-39-58.png
    upload_2018-1-18_16-39-58.png
    3.2 KB · Views: 927
  • upload_2018-1-18_16-41-29.png
    upload_2018-1-18_16-41-29.png
    52.6 KB · Views: 1,074
  • upload_2018-1-18_16-41-56.png
    upload_2018-1-18_16-41-56.png
    63.7 KB · Views: 949
  • upload_2018-1-18_16-42-33.png
    upload_2018-1-18_16-42-33.png
    21.6 KB · Views: 1,465
Physics news on Phys.org
One problem I can see with your work is where you write:
upload_2018-1-18_17-12-40.png

##(s^2 + 9) \neq (s - 3)(s + 3)##
 

Attachments

  • upload_2018-1-18_17-12-40.png
    upload_2018-1-18_17-12-40.png
    3.3 KB · Views: 452
Also,
s^2 + 6s + 8 does not factor to (s-2)(s-4). Poles in the rt-hand plane are bad business!
 
Cocoleia said:

Homework Statement


I am given this equation:
View attachment 218670
and asked to solve using Laplace transforms

The Attempt at a Solution


This is what I did:
View attachment 218671
View attachment 218672
This seemed logical to me, I used partial fractions and it stayed pretty simple.

This is what the solutions my prof posted do:
View attachment 218673

Is my answer equivalent to this, or are their faults in my logic and work ?
Their (sic) are faults in your work ...
 

Similar threads

Replies
5
Views
3K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 10 ·
Replies
10
Views
3K
Replies
10
Views
3K
Replies
7
Views
5K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 1 ·
Replies
1
Views
1K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 8 ·
Replies
8
Views
4K