P. 359, peak time derivation

The final result is correct, but there are multiple mistakes in the derivation of the peak time. The derivation should be:

$\frac{d}{dt}y(t)=\zeta {\omega }_n{e}^{-\zeta {\omega }_{n}t}(\cos {\omega }_{d}t+\frac{\zeta }{\sqrt{1-{\zeta }^2}}\sin {\omega }_{d}t)-e^{-\zeta {\omega }_{n}t}(-{\omega }_d\sin {\omega }_{d}t+\frac{\zeta {\omega }_d}{\sqrt{1-{\zeta }^2}}\cos {\omega }_{d}t)$

$\frac{d}{dt}y(t)=\zeta {\omega }_n{e}^{-\zeta {\omega }_{n}t}(\cos {\omega }_{d}t+\frac{\zeta }{\sqrt{1-{\zeta }^2}}\sin {\omega }_{d}t)-e^{-\zeta {\omega }_{n}t}(-{\omega }_d\sin {\omega }_{d}t+\zeta {\omega }_n\cos {\omega }_{d}t)$

$\frac{d}{dt}y(t)=(\frac{{\zeta }^2{\omega }_n}{\sqrt{1-{\zeta }^2}}+{\omega }_d)\sin {\omega }_{d}t.$

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