The sine function is equal to one at these five values of $\displaystyle\theta\usepackage{cmbright}\Huge\$ , but $\displaystyle{8}\pi+\frac{\pi}{{2}}\usepackage{cmbright}\Huge\$ is not in the interval $\displaystyle{0}\le\theta\le{8}\pi\usepackage{cmbright}\Huge\$ . Remember that the graph of sine has a hill/valley pattern that repeats forever in both directions. Each hill and valley pattern together is $\displaystyle{2}\pi\usepackage{cmbright}\Huge\$ units wide. Because of this, values of the function will repeat with regularity.