Chapter 5 - Trigonometric Functions - Section 5.4 Graphs of the Sine and Cosine Functions* - 5.4 Assess Your Understanding - Page 431: 12

$\text{Amplitude}= 3$ $\text{Period}=T= 2\pi$

Recall: For $y=A\cos{({\omega}x)}$, we have: $\text{Amplitude}=|A|$ and $\text{Period}=T=\frac{2\pi}{\omega}$ In $y=3\cos x$, we have $A=3$ and $\omega=1$, so $\text{Amplitude} =|3|=3$ $\text{Period}=T=\frac{2\pi}{\omega}=\frac{2\pi}{1}=2\pi$