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Laplace & Inverse Laplace Transforms

 
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Oct19-08, 07:05 PM   #1
 

Laplace & Inverse Laplace Transforms


1. The problem statement, all variables and given/known data
L[f(t)]= 1/(s^2+1)^2 + 1/(s^2+1)
L[f(t)]= ln(s+a) where 'a' is a constant


2. Relevant equations



3. The attempt at a solution
I know that the inverse laplace of 1/(s^2+1) is sin(t), but how do I deal with the squared form of it.

I have never encountered a logarithmic funcion for laplace, so can it be inverted back to f(t) with some of the common solution of conversion?

Thanks
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Oct20-08, 12:49 AM   #2
 
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Quote by 2RIP View Post
1. The problem statement, all variables and given/known data
L[f(t)]= 1/(s^2+1)^2 + 1/(s^2+1)
L[f(t)]= ln(s+a) where 'a' is a constant


2. Relevant equations



3. The attempt at a solution
I know that the inverse laplace of 1/(s^2+1) is sin(t), but how do I deal with the squared form of it.

I have never encountered a logarithmic funcion for laplace, so can it be inverted back to f(t) with some of the common solution of conversion?

Thanks
For the first problem, and using a table of Laplace transforms, I see that:
L(1/(2w^2)(sin (wt) - wt cos(wt)) = 1/(s^2 + w^2)^2
and L(sin(wt)) = w/(s^2 + w^2)

I'm stumped on the other problem
Oct20-08, 06:27 AM   #3
 
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No elementary function has ln(s+a) as its Laplace transform.
Oct21-08, 12:18 AM   #4
 

Laplace & Inverse Laplace Transforms


f(t) = (-t)^n[f(t)]
F(s) = F(s)^nth derivative

I believe that's what I got to do for the second one. thanks
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