# P. 256, lines -5 and -6

${\displaystyle \xi (t)=c_{1}\left({\begin{bmatrix}0\\\omega _{n_{1}}\\0\\\omega _{n_{1}}\end{bmatrix}}\cos \omega _{n_{1}}t+\left[{\begin{array}{c}1\\0\\1\\0\end{array}}\right]\sin \omega _{n_{1}}t\right)+c_{2}\left({\begin{bmatrix}0\\\omega _{n_{1}}\\0\\\omega _{n_{1}}\end{bmatrix}}\sin \omega _{n_{1}}t-{\begin{bmatrix}1\\0\\1\\0\end{bmatrix}}\!\cos \omega _{n_{1}}t\right)+c_{3}\left({\begin{bmatrix}0\\-\omega _{n_{2}}\\0\\\omega _{n_{2}}\end{bmatrix}}\!\cos \omega _{n_{2}}t+{\begin{bmatrix}-1\\0\\1\\0\end{bmatrix}}\!\sin \omega _{n_{2}}t\right)+c_{4}\left({\begin{bmatrix}0\\-\omega _{n_{1}}\\0\\\omega _{n_{2}}\end{bmatrix}}\!\sin \omega _{n_{2}}t+{\begin{bmatrix}1\\0\\-1\\0\end{bmatrix}}\!\cos \omega _{n_{2}}t\right).}$