Solve y′′+y′+y=sin(x) with y(0)=0 and y′(0)=1 with Laplace Transformation

Jean Farrell

Jean Farrell

Answered question

2022-09-24

Solve y + y + y = sin ( x ) with y ( 0 ) = 0 and y ( 0 ) = 1 with Laplace Transformation
I solve it using the Laplace Transform:
L ( y + y + y ) = L ( sin ( x ) )
s 2 L ( y ) s y ( 0 ) y ( 0 ) + s L ( y ) y ( 0 ) + L ( y ) = 1 s 2 + 1
L ( y ) ( s 2 + s + 1 ) = 1 s 2 + 1 + 1
L ( y ) = s 2 + 2 s 2 + 1 1 ( s 2 + s + 1 )
What is the best way to get y(x)?

Answer & Explanation

seguidora1e

seguidora1e

Beginner2022-09-25Added 8 answers

L ( y ) ( s 2 + s + 1 ) = 1 s 2 + 1 + 1
L ( y ) = 1 ( s 2 + 1 ) ( ( s 2 + s + 1 ) ) + 1 ( s 2 + s + 1 ) = h ( s ) + g ( s )
Note that
g ( s ) = 1 ( s 2 + s + 1 ) = 1 ( s + 1 2 ) 2 + 3 4 = 2 3 3 2 ( s + 1 2 ) 2 + 3 4
Use the formula
L ( e a t sin ( b t ) ) = b ( s a ) 2 + b 2
L 1 ( g ( s ) ) = 2 3 e t / 2 sin ( 3 2 t )
Use fraction decomposition for the first fraction h ( s )
h ( s ) = 1 ( s 2 + 1 ) ( ( s 2 + s + 1 ) ) = s ( s 2 + 1 ) + s + 1 ( s 2 + s + 1 )
h ( s ) = s ( s 2 + 1 ) + s + 1 2 ( s + 1 2 ) 2 + 3 4 + 1 2 g ( s )
First fraction is laplace transform of cos t
For the the second fraction use the following formula
L ( e a t cos ( b t ) ) = s a ( s a ) 2 + b 2
Third fraction is just 1 2 g ( s )
Finally
y ( t ) = cos ( t ) + 3 3 e t / 2 sin ( 3 2 t ) + e t / 2 cos ( 3 2 t )

Do you have a similar question?

Recalculate according to your conditions!

New Questions in Differential Equations

Ask your question.
Get an expert answer.

Let our experts help you. Answer in as fast as 15 minutes.

Didn't find what you were looking for?