The equation should be
x ¨ + 2 ζ ω n x ˙ + ω n 2 x = F m cos ω t {\displaystyle {\ddot {x}}+2\zeta \omega _{n}{\dot {x}}+\omega _{n}^{2}x={\frac {F}{m}}\cos \omega t} .
Return to errata.
