Chapter 4 - Section 4.5 - Graphs of Sine and Cosine Functions - Exercise Set - Page 596: 50

Please see below.

Please note that a cosine function $y=A\cos (Bx-C)$ has amplitude $|A|$, period $\frac{2\pi }{B}$, and phase shift $\frac{C}{B}$. So the function $y=-4\cos (2x-\frac{\pi }{2} )$ has amplitude $|-4|=4$, period $\frac{2\pi }{2 }=\pi$, and phase shift $\frac{\frac{\pi }{2}}{2}=\frac{\pi }{4}$.