Answer
$y=-4$cos$(\frac{3}{2}(x+\frac{2\pi}{3}))$
Work Step by Step
The amplitude is half the distance between the minimum and maximum values of the function. Since the minimum is $-4$ and the maximum is $4$, $\frac{4-(-4)}{2}=4$ Also, since the function is inverted, there is a negative sign at the beginning.
The period is the interval needed to complete one cycle, and it is given by $k=\frac{2\pi}{p}$, where $p$ is the period and $k$ is the horizontal length of a function when it completes one cycle. Since the length, in this case, is $\frac{4\pi}{3}$, $k=\frac{2\pi}{4\pi/3}=\frac{3}{2}$
Horizontal shift is the amount of units the function has displaced horizontally. Since the sine function starts at the origin, the function has displaced $-2\pi/3$
