69.1.120 problem 171

Internal problem ID [14194]
Book : DIFFERENTIAL and INTEGRAL CALCULUS. VOL I. by N. PISKUNOV. MIR PUBLISHERS, Moscow 1969.
Section : Chapter 8. Differential equations. Exercises page 595
Problem number : 171
Date solved : Wednesday, March 05, 2025 at 10:39:31 PM
CAS classification : system_of_ODEs

\begin{align*} \frac {d}{d t}x \left (t \right )&=x \left (t \right )-2 y \left (t \right )\\ \frac {d}{d t}y \left (t \right )&=x \left (t \right )-y \left (t \right ) \end{align*}

With initial conditions

\begin{align*} x \left (0\right ) = 1\\ y \left (0\right ) = 1 \end{align*}

✓ Maple. Time used: 0.028 (sec). Leaf size: 16

ode:=[diff(x(t),t) = x(t)-2*y(t), diff(y(t),t) = x(t)-y(t)]; 
ic:=x(0) = 1y(0) = 1; 
dsolve([ode,ic]);
 

\begin{align*} x \left (t \right ) &= \cos \left (t \right )-\sin \left (t \right ) \\ y \left (t \right ) &= \cos \left (t \right ) \\ \end{align*}

✓ Mathematica. Time used: 0.006 (sec). Leaf size: 17

ode={D[x[t],t]==x[t]-2*y[t],D[y[t],t]==x[t]-y[t]}; 
ic={x[0]==1,y[0]==1}; 
DSolve[{ode,ic},{x[t],y[t]},t,IncludeSingularSolutions->True]
 

\begin{align*} x(t)\to \cos (t)-\sin (t) \\ y(t)\to \cos (t) \\ \end{align*}

✓ Sympy. Time used: 0.096 (sec). Leaf size: 27

from sympy import * 
t = symbols("t") 
x = Function("x") 
y = Function("y") 
ode=[Eq(-x(t) + 2*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)
 

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