A typo in equation (6.24).

For \(\zeta<1\,\), the corresponding equation should be\[y(t)=k\Big(1-e^{-\zeta\omega_0t}\cos{\omega_dt}-\frac{\zeta}{\sqrt{1-\zeta^2}}e^{-\zeta\omega_0t}\sin{\omega_dt}\Big)\].

--Shuo