You may have thought that the 4 in $\displaystyle{\cos{{4}}}{x}\usepackage{cmbright}\Huge\$ would make the period 4 times greater, but it does just the opposite. The period of $\displaystyle{y}={a}{\cos{{b}}}{x}\usepackage{cmbright}\Huge\$ is given by $\displaystyle\frac{{{2}\pi}}{{\left|{b}\right|}}\usepackage{cmbright}\Huge\$ .