## Precalculus (6th Edition) Blitzer

$d=-8 \cos \pi t$
Amplitude, $A=-8$ (negative because the object is moving down initially.) Given: $Period =2$ Now, period, $P=\dfrac{2 \pi}{\omega} \implies \omega =\dfrac{2 \pi}{2}=\pi$ So, $d=A \cos \omega t=-8 \cos \pi t$