Internal problem ID [340]
Book: Differential equations and linear algebra, 4th ed., Edwards and Penney
Section: Section 7.3, The eigenvalue method for linear systems. Page 395
Problem number: problem 26.
ODE order: 1.
ODE degree: 1.
Solve \begin {align*} x_{1}^{\prime }\relax (t )&=3 x_{1} \relax (t )+x_{3} \relax (t )\\ x_{2}^{\prime }\relax (t )&=9 x_{1} \relax (t )-x_{2} \relax (t )+2 x_{3} \relax (t )\\ x_{3}^{\prime }\relax (t )&=-9 x_{1} \relax (t )+4 x_{2} \relax (t )-x_{3} \relax (t ) \end {align*}
With initial conditions \[ [x_{1} \relax (0) = 0, x_{2} \relax (0) = 0, x_{3} \relax (0) = 17] \]
✓ Solution by Maple
Time used: 0.109 (sec). Leaf size: 64
dsolve([diff(x__1(t),t) = 3*x__1(t)+x__3(t), diff(x__2(t),t) = 9*x__1(t)-x__2(t)+2*x__3(t), diff(x__3(t),t) = -9*x__1(t)+4*x__2(t)-x__3(t), x__1(0) = 0, x__2(0) = 0, x__3(0) = 17],[x__1(t), x__2(t), x__3(t)], singsol=all)
\[ x_{1} \relax (t ) = {\mathrm e}^{-t} \sin \relax (t )-4 \,{\mathrm e}^{-t} \cos \relax (t )+4 \,{\mathrm e}^{3 t} \] \[ x_{2} \relax (t ) = -9 \,{\mathrm e}^{-t} \cos \relax (t )-2 \,{\mathrm e}^{-t} \sin \relax (t )+9 \,{\mathrm e}^{3 t} \] \[ x_{3} \relax (t ) = 17 \,{\mathrm e}^{-t} \cos \relax (t ) \]
✓ Solution by Mathematica
Time used: 0.017 (sec). Leaf size: 62
DSolve[{x1'[t]==3*x1[t]+0*x2[t]+1*x3[t],x2'[t]==9*x1[t]-1*x2[t]+2*x3[t],x3'[t]==-9*x1[t]+4*x2[t]-1*x3[t]},{x1[0]==0,x2[0]==0,x3[0]==17},{x1[t],x2[t],x3[t]},t,IncludeSingularSolutions -> True]
\begin{align*} \text {x1}(t)\to e^{-t} \left (4 e^{4 t}+\sin (t)-4 \cos (t)\right ) \\ \text {x2}(t)\to e^{-t} \left (9 e^{4 t}-2 \sin (t)-9 \cos (t)\right ) \\ \text {x3}(t)\to 17 e^{-t} \cos (t) \\ \end{align*}