Solve the differential equation using Laplace transformation x''+4x=e^(-t^2), t >= 0, x(0)=0,x′(0)=0

Davirnoilc

Davirnoilc

Answered question

2022-11-18

Solve the differential equation using Laplace transformation
x + 4 x = e t 2 ,   t 0 ,     x ( 0 ) = 0 , x ( 0 ) = 0
Write your answer as an integral. The hint suggests using convolution, but I'm not sure how to write e t 2 in terms of that. I'm only confused on this part. I can do the rest of the problem.

Answer & Explanation

Savion Chaney

Savion Chaney

Beginner2022-11-19Added 14 answers

So far, this is my solution to the differential equation after receiving advice.
Taking the Laplace transform of each side yields
( s 2 ) X ( s ) s ( x ( 0 ) ) x ( 0 ) + 4 X ( s ) = 0 e ( s t + t 2 ) d t
With X(s) being the Laplace transform of x(t) Plugging in the initial conditions yields ( s 2 ) X ( s ) + 4 X ( s ) = 0 e ( s t + t 2 ) d t Then, solving for X ( s ), X ( s )= 0 e ( s t + t 2 ) d t $ s 2 + 4
Knowing that the Laplace transform of e ( t 2 ) being 0 e ( s t + t 2 ) d t and that the Laplace transform of 1 2 sin ( 2 t ) is 1 ( s 2 + 4 ) , I get through convolution:
x ( t ) = 1 2 0 t s i n ( 2 t 2 τ ) ) e ( τ 2 ) d τ
Frances Pham

Frances Pham

Beginner2022-11-20Added 5 answers

Your main problem is how to find the Laplace of exp ( t 2 ). So that
0 e t 2 s t d t = 0 e ( t 2 + s t ) d t = e 1 4 s 2 0 e ( t + 1 2 s ) 2 d t = e 1 4 s 2 s 2 e u 2 d t = e 1 4 s 2 [ 0 e u 2 d t 0 s 2 e u 2 d t ] = e 1 4 s 2 [ π 2 π 2 e r f ( s 2 ) ] , s > 0
where e r f ( x ) = 2 π 0 x e u 2 d t is the error function.

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