76.8.10 problem 10

Internal problem ID [17499]
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 : 10
Date solved : Tuesday, January 28, 2025 at 10:39:34 AM
CAS classification : system_of_ODEs

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

✓ Solution by Maple

Time used: 0.075 (sec). Leaf size: 34

dsolve([diff(x(t),t) = -3*x(t)+2*y(t), diff(y(t),t) = -x(t)-y(t), x(0) = 1, y(0) = -2], singsol=all)
 

\begin{align*} x \left (t \right ) &= {\mathrm e}^{-2 t} \left (-5 \sin \left (t \right )+\cos \left (t \right )\right ) \\ y \left (t \right ) &= \frac {{\mathrm e}^{-2 t} \left (-6 \sin \left (t \right )-4 \cos \left (t \right )\right )}{2} \\ \end{align*}

✓ Solution by Mathematica

Time used: 0.007 (sec). Leaf size: 37

DSolve[{D[x[t],t]==-3*x[t]+2*y[t],D[y[t],t]==-x[t]-y[t]},{x[0]==1,y[0]==-2},{x[t],y[t]},t,IncludeSingularSolutions -> True]
 

\begin{align*} x(t)\to e^{-2 t} (\cos (t)-5 \sin (t)) \\ y(t)\to -e^{-2 t} (3 \sin (t)+2 \cos (t)) \\ \end{align*}