The maximum value of the cosine function is 1, and it occurs at the top of each hill in the graph. In the interval $\displaystyle{\left[-{2}\pi,{2}\pi\right]}\usepackage{cmbright}\Huge\$ , there are three hilltops: at $\displaystyle\theta=-{2}\pi,{0},\usepackage{cmbright}\Huge\$ and $\displaystyle{2}\pi\usepackage{cmbright}\Huge\$ .