Answer
please see image
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Work Step by Step
1. Start with the parent function $f(x)=\cos x$
(Graph:red dashed , amplitude 1, period $ 2\pi$)
If plotting by hand, use Table 2 on page 420 to plot 13 points on $[0,2\pi]$,
2. The graph of $-\displaystyle \frac{2}{3}\cos x=-\frac{2}{3}f(x)$ is obtained from f(x) by
reflecting f(x) about the x-axis $y=-f(x)$ , (green),
then vertically compressing that graph by factor $\displaystyle \frac{2}{3}$.
The new amplitude is $\displaystyle \frac{2}{3}$. Period remains same.
Graphing utility used: online calculator desmos.com.
The "wrench" button is used to set viewing window settings:
radians, step $\pi/2$, ... (see image below)
The accompanying table gives a sufficient number of points for graphing by hand.
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