A typo in equation (6.24).

For $\zeta <1\,$, the corresponding equation should be:

$y(t)=k{\Big (}1-e^{-\zeta \omega _{0}t}\cos {\omega _{d}t}-{\frac {\zeta }{\sqrt {1-\zeta ^{2}}}}e^{-\zeta \omega _{0}t}\sin {\omega _{d}t}{\Big )}$.

--Shuo