## Precalculus (6th Edition) Blitzer

$y= -\dfrac{1}{4} \sin (\dfrac{2 \pi x}{5})$
Amplitude, $A=-\dfrac{1}{4}$. It is negative because the object is "pulled down". Now, period, $P=\dfrac{2 \pi}{\omega}=5$ $\implies \omega=\dfrac{2 \pi}{5}$ Hence, the displacement of the particles after $x$ seconds can be written as: $y= -\dfrac{1}{4} \sin (\dfrac{2 \pi x}{5})$