Answer
See graph and explanations.
Work Step by Step
Given $y=3cos(2x)$, we can identify its period as $p=\frac{2\pi}{2}=\pi$. To graph the function, start from $y=cos(2x)$ (green curve), shrink horizontally by a factor of 2, then stretch vertically by a factor of 3 to get the red curve for $y=3cos(2x)$ as shown in the figure.
