1)Find the Laplace transform of 4e^2 t−3 cos^2(2t)+2 cosh(3t). 2)Find inverse Laplace transform of: (6s-4)/(s^2-4s+20) 3) (4s+12)/(s^2+8s+16)

independanteng

independanteng

Answered question

2022-10-31

1)Find the Laplace transform of
4 e 2 t 3 cos 2 ( 2 t ) + 2 cosh ( 3 t ) .
2)Find inverse Laplace transform of: 6 s 4 s 2 4 s + 20
3) 4 s + 12 s 2 + 8 s + 16

Answer & Explanation

Reese Hobbs

Reese Hobbs

Beginner2022-11-01Added 13 answers

1)Observing that cos 2 ( 2 t ) = 1 + cos ( 4 t ) 2 we have
L { cos 2 ( 2 t ) } = L { 1 2 + 1 2 cos ( 4 t ) } = 1 2 s + 1 2 s s 2 + 16
Thus the Laplace transform of f ( t ) = 4 e 2 t 3 cos 2 ( 2 t ) + 2 cosh ( 3 t ) is
F ( s ) = 4 s 2 3 2 s 3 2 s s 2 + 16 + 2 s s 2 9
2)We can write
G ( s ) = 6 s 4 s 2 4 s + 20 = 6 ( s 2 ) + 8 ( s 2 ) 2 + 16 = 6 ( s 2 ) ( s 2 ) 2 + 16 + 2 4 ( s 2 ) 2 + 16
and then
L 1 { G ( s ) } = g ( t ) = 6 e 2 t cos ( 4 t ) + 2 e 2 t sin ( 4 t ) = 2 e 2 t [ 3 cos ( 4 t ) + sin ( 4 t ) ]
3)We can write
H ( s ) = 4 s + 12 s 2 + 8 s + 16 = 4 ( s + 4 ) 4 ( s + 4 ) 2 = 4 s + 4 4 ( s + 4 ) 2
and then
L 1 { H ( s ) } = h ( t ) = 4 e 4 t 4 t e 4 t = 4 e 4 t ( 1 t )

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