On the interval $\displaystyle{\left[\pi,{4}\pi\right]}\usepackage{cmbright}\Huge\$ , the graph of sine has the following pattern: valley, hill, valley. The function attains its minimum value of $\displaystyle-{1}\usepackage{cmbright}\Huge\$ at the two low points of the two valleys. These points occur where $\displaystyle\theta=\frac{{{3}\pi}}{{2}}\usepackage{cmbright}\Huge\$ and $\displaystyle\theta=\frac{{{7}\pi}}{{2}}\usepackage{cmbright}\Huge\$ .