Answer
Please see below.
Work Step by Step
Please note that a cosine function $y=A\cos Bx$ has amplitude $|A|$ and period $\frac{2\pi }{B}$.
So the function $y=\cos 4x$ has amplitude $|1|=1$ and period $\frac{2\pi }{4 }=\frac{\pi }{2}$.
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