How to quickly compute the inverse laplace transform of (1)/((s^2+1)^2)

Tara Mayer

Tara Mayer

Answered question

2022-10-26

How to quickly compute the inverse laplace transform of 1 ( s 2 + 1 ) 2

Answer & Explanation

dippoliticsxu

dippoliticsxu

Beginner2022-10-27Added 9 answers

I guess you know the rule
L 1 [ f ( s ) ] ( t ) = t L 1 [ f ( s ) ] ( t )
and the fact that
L 1 [ 1 s 2 + 1 ] ( t ) = sin ( t )
and
L 1 [ s s 2 + 1 ] ( t ) = cos ( t ) ?
Now observe that
d d s ( s s 2 + 1 ) = 1 ( s 2 + 1 ) + 2 ( s 2 + 1 ) 2
and thus
1 ( s 2 + 1 ) 2 = 1 2 d d s ( s s 2 + 1 ) + 1 2 1 ( s 2 + 1 )
Using these results, we obtain
L 1 [ 1 ( s 2 + 1 ) 2 ] ( t ) = 1 2 t L 1 [ s s 2 + 1 ] ( t ) + 1 2 sin t = t cos t + sin t 2
racmanovcf

racmanovcf

Beginner2022-10-28Added 2 answers

f ( t ) = 0 t cos ( t u ) cos u d u
= 0 t ( cos t cos 2 u + sin t sin u cos u ) d u
cos t 0 t 1 + cos 2 u 2 d u + sin t 0 t sin u d sin u

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