70.25.5 problem 5

Internal problem ID [19104]
Book : Differential equations. An introduction to modern methods and applications. James Brannan, William E. Boyce. Third edition. Wiley 2015
Section : Chapter 6. Systems of First Order Linear Equations. Section 6.3 (Homogeneous Linear Systems with Constant Coefficients). Problems at page 408
Problem number : 5
Date solved : Thursday, October 02, 2025 at 03:38:00 PM
CAS classification : system_of_ODEs

\begin{align*} \frac {d}{d t}x_{1} \left (t \right )&=x_{1} \left (t \right )+x_{2} \left (t \right )+6 x_{3} \left (t \right )\\ \frac {d}{d t}x_{2} \left (t \right )&=x_{1} \left (t \right )+6 x_{2} \left (t \right )+x_{3} \left (t \right )\\ \frac {d}{d t}x_{3} \left (t \right )&=6 x_{1} \left (t \right )+x_{2} \left (t \right )+x_{3} \left (t \right ) \end{align*}

✓ Maple. Time used: 0.126 (sec). Leaf size: 63

ode:=[diff(x__1(t),t) = x__1(t)+x__2(t)+6*x__3(t), diff(x__2(t),t) = x__1(t)+6*x__2(t)+x__3(t), diff(x__3(t),t) = 6*x__1(t)+x__2(t)+x__3(t)]; 
dsolve(ode);
 

\begin{align*} x_{1} \left (t \right ) &= c_1 \,{\mathrm e}^{-5 t}+c_2 \,{\mathrm e}^{8 t}+c_3 \,{\mathrm e}^{5 t} \\ x_{2} \left (t \right ) &= c_2 \,{\mathrm e}^{8 t}-2 c_3 \,{\mathrm e}^{5 t} \\ x_{3} \left (t \right ) &= -c_1 \,{\mathrm e}^{-5 t}+c_2 \,{\mathrm e}^{8 t}+c_3 \,{\mathrm e}^{5 t} \\ \end{align*}

✓ Mathematica. Time used: 0.004 (sec). Leaf size: 163

ode={D[x1[t],t]==1*x1[t]+1*x2[t]+6*x3[t],D[x2[t],t]==1*x1[t]+6*x2[t]+1*x3[t],D[x3[t],t]==6*x1[t]+1*x2[t]+1*x3[t]}; 
ic={}; 
DSolve[{ode,ic},{x1[t],x2[t],x3[t]},t,IncludeSingularSolutions->True]
 

\begin{align*} \text {x1}(t)&\to \frac {1}{6} e^{-5 t} \left (c_1 \left (e^{10 t}+2 e^{13 t}+3\right )+(c_3-2 c_2) e^{10 t}+2 (c_2+c_3) e^{13 t}-3 c_3\right )\\ \text {x2}(t)&\to \frac {1}{3} e^{5 t} \left (c_1 \left (e^{3 t}-1\right )+c_2 \left (e^{3 t}+2\right )+c_3 \left (e^{3 t}-1\right )\right )\\ \text {x3}(t)&\to \frac {1}{6} e^{-5 t} \left (c_1 \left (e^{10 t}+2 e^{13 t}-3\right )+(c_3-2 c_2) e^{10 t}+2 (c_2+c_3) e^{13 t}+3 c_3\right ) \end{align*}

✓ Sympy. Time used: 0.086 (sec). Leaf size: 61

from sympy import * 
t = symbols("t") 
x__1 = Function("x__1") 
x__2 = Function("x__2") 
x__3 = Function("x__3") 
ode=[Eq(-x__1(t) - x__2(t) - 6*x__3(t) + Derivative(x__1(t), t),0),Eq(-x__1(t) - 6*x__2(t) - x__3(t) + Derivative(x__2(t), t),0),Eq(-6*x__1(t) - x__2(t) - x__3(t) + Derivative(x__3(t), t),0)] 
ics = {} 
dsolve(ode,func=[x__1(t),x__2(t),x__3(t)],ics=ics)
 

\[ \left [ x^{1}{\left (t \right )} = - C_{1} e^{- 5 t} + C_{2} e^{5 t} + C_{3} e^{8 t}, \ x^{2}{\left (t \right )} = - 2 C_{2} e^{5 t} + C_{3} e^{8 t}, \ x^{3}{\left (t \right )} = C_{1} e^{- 5 t} + C_{2} e^{5 t} + C_{3} e^{8 t}\right ] \]