The graph of cosine has one hill and one valley on the interval $\displaystyle{\left[-\frac{\pi}{{2}},\frac{{{3}\pi}}{{2}}\right]}\usepackage{cmbright}\Huge\$ . The hill covers the interval from $\displaystyle\theta=-\frac{\pi}{{2}}\usepackage{cmbright}\Huge\$ to $\displaystyle\theta=\frac{\pi}{{2}}\usepackage{cmbright}\Huge\$ . The highest point is in the middle of the hill: $\displaystyle{\left({0},{1}\right)}\usepackage{cmbright}\Huge\$ . The valley covers the interval from $\displaystyle\theta=\frac{\pi}{{2}}\usepackage{cmbright}\Huge\$ to $\displaystyle\theta=\frac{{{3}\pi}}{{2}}\usepackage{cmbright}\Huge\$ . The lowest point is in the middle of the valley: $\displaystyle{\left(\pi,-{1}\right)}\usepackage{cmbright}\Huge\$ .