Answer
$y=-4cos(3x)$
Work Step by Step
1. Based on the given graph, we can initially identify that it resembles a graph of negative cosine.
2. We can determine the amplitude $|A|=4$, period $p=\frac{2\pi}{3}$, passing $(0,-4)$.
3. Write a model as $y=-4cos(\omega x)$
4. We have $\frac{2\pi}{\omega}=\frac{2\pi}{3}$, thus $\omega=3$
5. The equation is $y=-4cos(3x)$
