P. 256, lines -5 and -6

The equation should be

$\xi (t)=c_1(\left[\begin{array}{c}0\\ {\omega }_{n_1}\\ 0\\ {\omega }_{n_1}\end{array}\right]\cos {\omega }_{n_1}t+\left[\begin{array}{c}1\\ 0\\ 1\\ 0\end{array}\right]\sin {\omega }_{n_1}t)+c_2(\left[\begin{array}{c}0\\ {\omega }_{n_1}\\ 0\\ {\omega }_{n_1}\end{array}\right]\sin {\omega }_{n_1}t-\left[\begin{array}{c}1\\ 0\\ 1\\ 0\end{array}\right]\cos {\omega }_{n_1}t)+c_3(\left[\begin{array}{c}0\\ -{\omega }_{n_2}\\ 0\\ {\omega }_{n_2}\end{array}\right]\cos {\omega }_{n_2}t+\left[\begin{array}{c}-1\\ 0\\ 1\\ 0\end{array}\right]\sin {\omega }_{n_2}t)+c_4(\left[\begin{array}{c}0\\ -{\omega }_{n_1}\\ 0\\ {\omega }_{n_2}\end{array}\right]\sin {\omega }_{n_2}t+\left[\begin{array}{c}1\\ 0\\ -1\\ 0\end{array}\right]\cos {\omega }_{n_2}t).$

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