14.26.15 problem 15

Internal problem ID [2788]
Book : Differential equations and their applications, 4th ed., M. Braun
Section : Chapter 3. Systems of differential equations. Section 3.13 (Solving systems by Laplace transform). Page 370
Problem number : 15
Date solved : Monday, January 27, 2025 at 06:13:52 AM
CAS classification : system_of_ODEs

\begin{align*} x_{1}^{\prime }\left (t \right )&=3 x_{1} \left (t \right )\\ x_{2}^{\prime }\left (t \right )&=x_{1} \left (t \right )+3 x_{2} \left (t \right )\\ x_{3}^{\prime }\left (t \right )&=3 x_{3} \left (t \right )\\ x_{4}^{\prime }\left (t \right )&=2 x_{3} \left (t \right )+3 x_{4} \left (t \right ) \end{align*}

With initial conditions

\begin{align*} x_{1} \left (0\right ) = 1\\ x_{2} \left (0\right ) = 1\\ x_{3} \left (0\right ) = 1\\ x_{4} \left (0\right ) = 1 \end{align*}

✓ Solution by Maple

Time used: 0.037 (sec). Leaf size: 39

dsolve([diff(x__1(t),t) = 3*x__1(t), diff(x__2(t),t) = x__1(t)+3*x__2(t), diff(x__3(t),t) = 3*x__3(t), diff(x__4(t),t) = 2*x__3(t)+3*x__4(t), x__1(0) = 1, x__2(0) = 1, x__3(0) = 1, x__4(0) = 1], singsol=all)
 

\begin{align*} x_{1} \left (t \right ) &= {\mathrm e}^{3 t} \\ x_{2} \left (t \right ) &= \left (t +1\right ) {\mathrm e}^{3 t} \\ x_{3} \left (t \right ) &= {\mathrm e}^{3 t} \\ x_{4} \left (t \right ) &= \left (1+2 t \right ) {\mathrm e}^{3 t} \\ \end{align*}

✓ Solution by Mathematica

Time used: 0.006 (sec). Leaf size: 44

DSolve[{D[x1[t],t]==3*x1[t],D[x2[t],t]==1*x1[t]+3*x2[t],D[x3[t],t]==3*x3[t],D[x4[t],t]==2*x3[t]+3*x4[t]},{x1[0]==1,x2[0]==1,x3[0]==1,x4[0]==1},{x1[t],x2[t],x3[t],x4[t]},t,IncludeSingularSolutions -> True]
 

\begin{align*} \text {x1}(t)\to e^{3 t} \\ \text {x2}(t)\to e^{3 t} (t+1) \\ \text {x3}(t)\to e^{3 t} \\ \text {x4}(t)\to e^{3 t} (2 t+1) \\ \end{align*}