78.5.12 problem 5.f

Internal problem ID [21051]
Book : A FIRST COURSE IN DIFFERENTIAL EQUATIONS FOR SCIENTISTS AND ENGINEERS. By Russell Herman. University of North Carolina Wilmington. LibreText. compiled on 06/09/2025
Section : Chapter 6, Linear systems. Problems section 6.9
Problem number : 5.f
Date solved : Thursday, October 02, 2025 at 07:01:47 PM
CAS classification : system_of_ODEs

\begin{align*} x^{\prime }\left (t \right )&=x \left (t \right )-y\\ y^{\prime }&=x \left (t \right )+y \end{align*}

✓ Maple. Time used: 0.139 (sec). Leaf size: 33

ode:=[diff(x(t),t) = x(t)-y(t), diff(y(t),t) = x(t)+y(t)]; 
dsolve(ode);
 

\begin{align*} x \left (t \right ) &= {\mathrm e}^{t} \left (c_2 \cos \left (t \right )+c_1 \sin \left (t \right )\right ) \\ y \left (t \right ) &= -{\mathrm e}^{t} \left (\cos \left (t \right ) c_1 -\sin \left (t \right ) c_2 \right ) \\ \end{align*}

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

ode={D[x[t],t]==x[t]-y[t],D[y[t],t]==x[t]+y[t]}; 
ic={}; 
DSolve[{ode,ic},{x[t],y[t]},t,IncludeSingularSolutions->True]
 

\begin{align*} x(t)&\to e^t (c_1 \cos (t)-c_2 \sin (t))\\ y(t)&\to e^t (c_2 \cos (t)+c_1 \sin (t)) \end{align*}

✓ Sympy. Time used: 0.049 (sec). Leaf size: 39

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

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