Answer:
The solution of the diferential equation is:
![y(t)=\frac{1}{2}cos(t)- \frac{1}{2}e^{t}+\frac{t}{2} e^{t}](https://tex.z-dn.net/?f=y%28t%29%3D%5Cfrac%7B1%7D%7B2%7Dcos%28t%29-%20%5Cfrac%7B1%7D%7B2%7De%5E%7Bt%7D%2B%5Cfrac%7Bt%7D%7B2%7D%20e%5E%7Bt%7D)
Step-by-step explanation:
Given
; y(0) = 0 ; y'(0) = 0
We need to use the Laplace transform to solve it.
ℒ[y" + y]=ℒ[
]
ℒ[y"]+ℒ[y]=ℒ[
]
By using the Table of Laplace Transform we get:
ℒ[y"]=s²·ℒ[y]+s·y(0)-y'(0)=s²·Y(s)
ℒ[y]=Y(s)
ℒ[
]=![\frac{1}{(s-1)^{2}}](https://tex.z-dn.net/?f=%5Cfrac%7B1%7D%7B%28s-1%29%5E%7B2%7D%7D)
So, the transformation is equal to:
s²·Y(s)+Y(s)=![\frac{1}{(s-1)^{2}}](https://tex.z-dn.net/?f=%5Cfrac%7B1%7D%7B%28s-1%29%5E%7B2%7D%7D)
(s²+1)·Y(s)=![\frac{1}{(s-1)^{2}}](https://tex.z-dn.net/?f=%5Cfrac%7B1%7D%7B%28s-1%29%5E%7B2%7D%7D)
Y(s)=![\frac{1}{(s^{2}+1)(s-1)^{2}}](https://tex.z-dn.net/?f=%5Cfrac%7B1%7D%7B%28s%5E%7B2%7D%2B1%29%28s-1%29%5E%7B2%7D%7D)
To be able to separate in terms, we use the partial fraction method:
![\frac{1}{(s^{2}+1)(s-1)^{2}}=\frac{As+B}{s^{2}+1} +\frac{C}{s-1}+\frac{D}{(s-1)^2}](https://tex.z-dn.net/?f=%5Cfrac%7B1%7D%7B%28s%5E%7B2%7D%2B1%29%28s-1%29%5E%7B2%7D%7D%3D%5Cfrac%7BAs%2BB%7D%7Bs%5E%7B2%7D%2B1%7D%20%2B%5Cfrac%7BC%7D%7Bs-1%7D%2B%5Cfrac%7BD%7D%7B%28s-1%29%5E2%7D)
1=(As+B)(s-1)² + C(s-1)(s²+1)+ D(s²+1)
The equation is reduced to:
1=s³(A+C)+s²(B-2A-C+D)+s(A-2B+C)+(B+D-C)
With the previous equation we can make an equation system of 4 variables.
The system is given by:
A+C=0
B-2A-C+D=0
A-2B+C=0
B+D-C=1
The solution of the system is:
A=1/2 ; B=0 ; C=-1/2 ; D=1/2
Therefore, Y(s) is equal to:
Y(s)=![\frac{s}{2(s^{2} +1)} -\frac{1}{2(s-1)} +\frac{1}{2(s-1)^{2}}](https://tex.z-dn.net/?f=%5Cfrac%7Bs%7D%7B2%28s%5E%7B2%7D%20%2B1%29%7D%20-%5Cfrac%7B1%7D%7B2%28s-1%29%7D%20%2B%5Cfrac%7B1%7D%7B2%28s-1%29%5E%7B2%7D%7D)
By using the inverse of the Laplace transform:
ℒ⁻¹[Y(s)]=ℒ⁻¹[
]-ℒ⁻¹[
]+ℒ⁻¹[
]
![y(t)=\frac{1}{2}cos(t)- \frac{1}{2}e^{t}+\frac{t}{2} e^{t}](https://tex.z-dn.net/?f=y%28t%29%3D%5Cfrac%7B1%7D%7B2%7Dcos%28t%29-%20%5Cfrac%7B1%7D%7B2%7De%5E%7Bt%7D%2B%5Cfrac%7Bt%7D%7B2%7D%20e%5E%7Bt%7D)