P. 209, line -8

The equation should be:

$[\begin{matrix} ξ_{1} (t) \\ ξ_{2} (t) \end{matrix}] = k_{1} e^{t} ([\begin{matrix} 1 \\ 0 \end{matrix}] \cos 2 t - [\begin{matrix} 0 \\ - 1 \end{matrix}] \sin 2 t) + k_{2} e^{t} ([\begin{matrix} 1 \\ 0 \end{matrix}] \sin 2 t + [\begin{matrix} 0 \\ - 1 \end{matrix}] \cos 2 t)$