20.15.1 problem 1

Internal problem ID [3827]
Book : Differential equations and linear algebra, Stephen W. Goode and Scott A Annin. Fourth edition, 2015
Section : Chapter 9, First order linear systems. Section 9.3, page 598
Problem number : 1
Date solved : Tuesday, March 04, 2025 at 05:17:39 PM
CAS classification : system_of_ODEs

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

✓ Maple. Time used: 0.016 (sec). Leaf size: 34

ode:=[diff(x__1(t),t) = 3*x__2(t), diff(x__2(t),t) = -3*x__1(t)]; 
dsolve(ode);
 

\begin{align*} x_{1} \left (t \right ) &= \sin \left (3 t \right ) c_{1} +\cos \left (3 t \right ) c_{2} \\ x_{2} \left (t \right ) &= \cos \left (3 t \right ) c_{1} -\sin \left (3 t \right ) c_{2} \\ \end{align*}

✓ Mathematica. Time used: 0.002 (sec). Leaf size: 39

ode={D[x1[t],t]==3*x2[t],D[x2[t],t]==-3*x1[t]}; 
ic={}; 
DSolve[{ode,ic},{x1[t],x2[t]},t,IncludeSingularSolutions->True]
 

\begin{align*} \text {x1}(t)\to c_1 \cos (3 t)+c_2 \sin (3 t) \\ \text {x2}(t)\to c_2 \cos (3 t)-c_1 \sin (3 t) \\ \end{align*}

✓ Sympy. Time used: 0.067 (sec). Leaf size: 31

from sympy import * 
t = symbols("t") 
x__1 = Function("x__1") 
x__2 = Function("x__2") 
ode=[Eq(-3*x__2(t) + Derivative(x__1(t), t),0),Eq(3*x__1(t) + Derivative(x__2(t), t),0)] 
ics = {} 
dsolve(ode,func=[x__1(t),x__2(t)],ics=ics)
 

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