Answer
$3$, $\pi$, $-\frac{\pi}{2}$.
See graph.
Work Step by Step
1. Given $y=3cos(2x+\pi)=3cos[2(x+\frac{\pi}{2})]$, we can find the amplitude $|A|=3$, period $p=\frac{2\pi}{2}=\pi$, and phase shift $-\frac{\pi}{2}$.
2. See graph.
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