Equation 4.8 should be
x ( t ) = ( x 0 − δ 1 − r 2 ) cos ω n t + x ˙ 0 ω n sin ω n t + δ 1 − r 2 cos ω t {\displaystyle x(t)=\left(x_{0}-{\frac {\delta }{1-r^{2}}}\right)\cos \omega _{n}t+{\frac {{\dot {x}}_{0}}{\omega _{n}}}\sin \omega _{n}t+{\frac {\delta }{1-r^{2}}}\cos \omega t}
Return to errata.
