Question #183349

dx/dt=x-y dy/dt=x +3y

1
Expert's answer
2021-05-03T07:18:46-0400
dxdt=xy\dfrac{dx}{dt}=x-y

dydt=x+3y\dfrac{dy}{dt}=x+3y

(dx/dtdy/dt)=(1113)(xy)\begin{pmatrix} dx/dt \\ dy/dt \end{pmatrix}=\begin{pmatrix} 1 & -1 \\ 1 & 3 \end{pmatrix} \begin{pmatrix} x \\ y \end{pmatrix}

Find the eigenvalues 


(1λ113λ)=0\begin{pmatrix} 1-\lambda & -1 \\ 1 & 3-\lambda \end{pmatrix}=0

(1λ)(3λ)+1=0(1-\lambda)(3-\lambda)+1=0

λ24λ+4=0\lambda^2-4\lambda+4=0

λ1=λ2=2\lambda_1=\lambda_2=2

 Find the eigenvectors.

λ=2\lambda=2


(121132)(v1v2)=0\begin{pmatrix} 1-2 & -1 \\ 1 & 3-2 \end{pmatrix}\begin{pmatrix} v_1 \\ v_2 \end{pmatrix}=0

The eigen vector is


v=(11)v=\begin{pmatrix} -1 \\ 1 \end{pmatrix}

For repeated eigenvalues λ1=λ2=2\lambda_1=\lambda_2=2 and the eigenvector v=(11)v=\begin{pmatrix} -1 \\ 1 \end{pmatrix}

the general solution takes form


(xy)=c1e2t(11)+c2te2t(11)+c2e2t(u1u2)\begin{pmatrix} x \\ y \end{pmatrix}=c_1e^{2t}\begin{pmatrix} -1 \\ 1 \end{pmatrix}+c_2 te^{2t}\begin{pmatrix} -1 \\ 1 \end{pmatrix}+c_2e^{2t}\begin{pmatrix} u_1 \\ u_2 \end{pmatrix}

where


(121132)(u1u2)=(11)\begin{pmatrix} 1-2 & -1 \\ 1 & 3-2 \end{pmatrix}\begin{pmatrix} u_1 \\ u_2 \end{pmatrix}=\begin{pmatrix} -1 \\ 1 \end{pmatrix}

(u1u2)=(10)\begin{pmatrix} u_1 \\ u_2 \end{pmatrix}=\begin{pmatrix} 1 \\ 0 \end{pmatrix}

The solution is


(xy)=c1e2t(11)+c2te2t(11)+c2e2t(10)\begin{pmatrix} x \\ y \end{pmatrix}=c_1e^{2t}\begin{pmatrix} -1 \\ 1 \end{pmatrix}+c_2 te^{2t}\begin{pmatrix} -1 \\ 1 \end{pmatrix}+c_2e^{2t}\begin{pmatrix} 1 \\ 0 \end{pmatrix}


Need a fast expert's response?

Submit order

and get a quick answer at the best price

for any assignment or question with DETAILED EXPLANATIONS!

Comments

No comments. Be the first!
LATEST TUTORIALS
APPROVED BY CLIENTS