Use Laplace Transform to solve the following IVP: y′′+2y′+5y=e^(−t) sin(2t) where y(0)=2,y′(0)=−1

Layton Park

Layton Park

Answered question

2022-11-10

Use Laplace Transform to solve the following IVP:
y + 2 y + 5 y = e t sin ( 2 t ) where y ( 0 ) = 2 , y ( 0 ) = 1

Answer & Explanation

cismadmec

cismadmec

Beginner2022-11-11Added 22 answers

You need the inverse Laplace transform of
2 ( s 2 + 2 s + 5 ) 2
This may help:
L { t e a t cos ( b t ) } = ( s a ) 2 b 2 ( ( s a ) 2 + b 2 ) 2 = 1 ( s a ) 2 + b 2 2 b 2 ( ( s a ) 2 + b 2 ) 2
tramolatzqvg

tramolatzqvg

Beginner2022-11-12Added 3 answers

We can take inverse Laplace transform by using the Bromwich integral. That is,
L 1 { Y ( s ) } = 1 2 π i lim T γ i T γ + i T Y ( s ) e s t d s = Res
where
Y ( s ) = 2 ( s 2 + 2 s + 5 ) 2 + 2 s + 3 s 2 + 2 s + 5
Then the poles of s are at s = 1 ± 2 i. We can then evaluate the integrals by splitting them into two. In the first one, the poles are of order two.

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