P. 138, line 6 (large boxed equation)

The equation should be:

$x(t)=\frac{{\dot{x}}_0+x_0{\omega }_n(\zeta +\sqrt{{\zeta }^2-1})}{2{\omega }_n\sqrt{{\zeta }^2-1}}{e}^{(-\zeta {\omega }_n+{\omega }_n\sqrt{{\zeta }^2-1})t}-\frac{{\dot{x}}_0-x_0{\omega }_n(-\zeta +\sqrt{{\zeta }^2-1})}{2{\omega }_n\sqrt{{\zeta }^2-1}}{e}^{(-\zeta {\omega }_n-{\omega }_n\sqrt{{\zeta }^2-1})t}.$

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