Answer
Please see below.
Work Step by Step
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 $y=\frac{1}{2}\cos (2x+\pi )$ has amplitude $|\frac{1}{2}|=\frac{1}{2}$, period $\frac{2\pi }{2 }=\pi$, and phase shift $\frac{-\pi }{2}=-\frac{\pi }{2}$.
