View source for P. 256, lines -5 and -6

The equation should be

<math>
\xi(t) =  c_1 \left(\begin{bmatrix} 0 \\ \omega_{n_1} \\ 0 \\ \omega_{n_1} \end{bmatrix} \cos \omega_{n_1} t + \left[ \begin{array}{c} 1 \\ 0 \\ 1 \\ 0 \end{array} \right] \sin \omega_{n_1} t \right)  + 
          c_2 \left(\begin{bmatrix} 0 \\ \omega_{n_1} \\ 0 \\ \omega_{n_1} \end{bmatrix} \sin \omega_{n_1} t - \begin{bmatrix} 1 \\ 0 \\ 1 \\ 0 \end{bmatrix}\! \cos \omega_{n_1} t  \right) +  
          c_3 \left( \begin{bmatrix} 0 \\ -\omega_{n_2} \\ 0 \\ \omega_{n_2} \end{bmatrix}\! \cos \omega_{n_2} t +  \begin{bmatrix} -1 \\ 0 \\ 1 \\ 0 \end{bmatrix}\! \sin \omega_{n_2} t \right)  +
          c_4 \left(\begin{bmatrix} 0 \\ -\omega_{n_1} \\ 0 \\ \omega_{n_2} \end{bmatrix}\! \sin \omega_{n_2} t + \begin{bmatrix} 1 \\ 0 \\ -1 \\ 0 \end{bmatrix}\! \cos \omega_{n_2} t \right). 
</math>


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