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:

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

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

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

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