76.8.8 problem 8

Internal problem ID [17418]
Book : Differential equations. An introduction to modern methods and applications. James Brannan, William E. Boyce. Third edition. Wiley 2015
Section : Chapter 3. Systems of two first order equations. Section 3.4 (Complex Eigenvalues). Problems at page 177
Problem number : 8
Date solved : Thursday, March 13, 2025 at 10:08:01 AM
CAS classification : system_of_ODEs

\begin{align*} \frac {d}{d t}x \left (t \right )&=2 x \left (t \right )-5 y \left (t \right )\\ \frac {d}{d t}y \left (t \right )&=x \left (t \right )-2 y \left (t \right ) \end{align*}

With initial conditions

\begin{align*} x \left (0\right ) = 3\\ y \left (0\right ) = 2 \end{align*}

✓ Maple. Time used: 0.009 (sec). Leaf size: 25

ode:=[diff(x(t),t) = 2*x(t)-5*y(t), diff(y(t),t) = x(t)-2*y(t)]; 
ic:=x(0) = 3y(0) = 2; 
dsolve([ode,ic]);
 

\begin{align*} x \left (t \right ) &= -4 \sin \left (t \right )+3 \cos \left (t \right ) \\ y \left (t \right ) &= 2 \cos \left (t \right )-\sin \left (t \right ) \\ \end{align*}

✓ Mathematica. Time used: 0.007 (sec). Leaf size: 26

ode={D[x[t],t]==2*x[t]-5*y[t],D[y[t],t]==x[t]-2*y[t]}; 
ic={x[0]==3,y[0]==2}; 
DSolve[{ode,ic},{x[t],y[t]},t,IncludeSingularSolutions->True]
 

\begin{align*} x(t)\to 3 \cos (t)-4 \sin (t) \\ y(t)\to 2 \cos (t)-\sin (t) \\ \end{align*}

✓ Sympy. Time used: 0.092 (sec). Leaf size: 32

from sympy import * 
t = symbols("t") 
x = Function("x") 
y = Function("y") 
ode=[Eq(-2*x(t) + 5*y(t) + Derivative(x(t), t),0),Eq(-x(t) + 2*y(t) + Derivative(y(t), t),0)] 
ics = {} 
dsolve(ode,func=[x(t),y(t)],ics=ics)
 

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