The alternating pattern of hills and valleys repeats over every interval of length $\displaystyle{2}\pi\usepackage{cmbright}\Huge\$ , forever in both directions. From $\displaystyle\theta=-\pi\usepackage{cmbright}\Huge\$ to $\displaystyle\theta={0}\usepackage{cmbright}\Huge\$ , there is a valley. Moving $\displaystyle{2}\pi\usepackage{cmbright}\Huge\$ units to the left, there is a valley from $\displaystyle\theta=-{3}\pi\usepackage{cmbright}\Huge\$ to $\displaystyle\theta=-{2}\pi\usepackage{cmbright}\Huge\$ . Therefore, over the interval of length $\displaystyle{4}\pi\usepackage{cmbright}\Huge\$ from $\displaystyle\theta=-{3}\pi\usepackage{cmbright}\Huge\$ to $\displaystyle\theta=\pi\usepackage{cmbright}\Huge\$ , you get: valley, hill, valley, hill