P. 209, line -8

The equation should be:

$\left[\begin{array}{c}{\xi }_1(t)\\ {\xi }_2(t)\end{array}\right]=k_1{e}^t(\left[\begin{array}{c}1\\ 0\end{array}\right]\cos 2t-\left[\begin{array}{c}0\\ -1\end{array}\right]\sin 2t)+k_2{e}^t(\left[\begin{array}{c}1\\ 0\end{array}\right]\sin 2t+\left[\begin{array}{c}0\\ -1\end{array}\right]\cos 2t)$

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