This is a value of x where $\displaystyle{y}={\cos{{\left(\frac{{1}}{{2}}{x}\right)}}}\usepackage{cmbright}\Huge\$ is at its maximum, but it is not positive. The next point where the maximum occurs is at the end of one cycle. The value of x at that point is the length of one cycle, or one period of $\displaystyle{y}={\cos{{\left(\frac{{1}}{{2}}{x}\right)}}}\usepackage{cmbright}\Huge\$ .