# A typo in equation (6.24).

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