How to compute the Inverse Laplace of (1)/((s^2+a^2)^n)?

Kymani Hatfield

Kymani Hatfield

Answered question

2022-10-13

How to compute the Inverse Laplace of 1 ( s 2 + a 2 ) n ? I know that to compute Inverse Laplace 1 ( s 2 + a 2 ) 2 , the convolution Theorem is useful. but is there an interesting idea for general case?

Answer & Explanation

Davin Meyer

Davin Meyer

Beginner2022-10-14Added 13 answers

We could, also, use the definition
L 1 { F ( s ) } = 1 2 π i γ i γ + i e s t ( s 2 + a 2 ) n d s = Res
We have n poles at s = ± i a so
L 1 { F ( s ) } = lim s i a 1 ( n 1 ) ! d n 1 d s n 1 ( s i a ) n e s t ( s 2 + a 2 ) n + lim s i a 1 ( n 1 ) ! d n 1 d s n 1 ( s + i a ) n e s t ( s 2 + a 2 ) n
caritatsjq

caritatsjq

Beginner2022-10-15Added 3 answers

You can use the convolution theorem inductively:
L 1 [ 1 ( s 2 + a 2 ) n ] = L 1 [ 1 ( s 2 + a 2 ) n 1 ] L 1 [ 1 ( s 2 + a 2 ) ]
and we have the base case.
Hence
L 1 [ 1 ( s 2 + a 2 ) n ] = sin ( a x ) a sin ( a x ) a n  times

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