9.6.15 problem problem 15

Internal problem ID [1022]
Book : Differential equations and linear algebra, 4th ed., Edwards and Penney
Section : Section 7.6, Multiple Eigenvalue Solutions. Page 451
Problem number : problem 15
Date solved : Saturday, March 29, 2025 at 10:37:04 PM
CAS classification : system_of_ODEs

\begin{align*} \frac {d}{d t}x_{1} \left (t \right )&=-2 x_{1} \left (t \right )-9 x_{2} \left (t \right )\\ \frac {d}{d t}x_{2} \left (t \right )&=x_{1} \left (t \right )+4 x_{2} \left (t \right )\\ \frac {d}{d t}x_{3} \left (t \right )&=x_{1} \left (t \right )+3 x_{2} \left (t \right )+x_{3} \left (t \right ) \end{align*}

✓ Maple. Time used: 0.184 (sec). Leaf size: 46

ode:=[diff(x__1(t),t) = -2*x__1(t)-9*x__2(t), diff(x__2(t),t) = x__1(t)+4*x__2(t), diff(x__3(t),t) = x__1(t)+3*x__2(t)+x__3(t)]; 
dsolve(ode);
 

\begin{align*} x_{1} \left (t \right ) &= {\mathrm e}^{t} \left (c_3 t +c_2 \right ) \\ x_{2} \left (t \right ) &= -\frac {{\mathrm e}^{t} \left (3 c_3 t +3 c_2 +c_3 \right )}{9} \\ x_{3} \left (t \right ) &= \frac {{\mathrm e}^{t} \left (-c_3 t +3 c_1 -c_2 \right )}{3} \\ \end{align*}

✓ Mathematica. Time used: 0.003 (sec). Leaf size: 62

ode={D[ x1[t],t]==-2*x1[t]-9*x2[t]-0*x3[t],D[ x2[t],t]==1*x1[t]+4*x2[t]-0*x3[t],D[ x3[t],t]==1*x1[t]+3*x2[t]+1*x3[t]}; 
ic={}; 
DSolve[{ode,ic},{x1[t],x2[t],x3[t]},t,IncludeSingularSolutions->True]
 

\begin{align*} \text {x1}(t)\to -e^t (c_1 (3 t-1)+9 c_2 t) \\ \text {x2}(t)\to e^t ((c_1+3 c_2) t+c_2) \\ \text {x3}(t)\to e^t ((c_1+3 c_2) t+c_3) \\ \end{align*}

✓ Sympy. Time used: 0.129 (sec). Leaf size: 53

from sympy import * 
t = symbols("t") 
x__1 = Function("x__1") 
x__2 = Function("x__2") 
x__3 = Function("x__3") 
ode=[Eq(2*x__1(t) + 9*x__2(t) + Derivative(x__1(t), t),0),Eq(-x__1(t) - 4*x__2(t) + Derivative(x__2(t), t),0),Eq(-x__1(t) - 3*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)
 

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