Unit circle

On the unit circle, every point is $(\cos \theta ,\sin \theta )$ where $\theta$ is measured counterclockwise from the positive $x$-axis. The cosine is the $x$-coordinate and the sine is the $y$-coordinate. For angles beyond $90^{\circ }$, find the reference angle—the acute angle the terminal side makes with the $x$-axis—and assign signs by quadrant: Quadrant I $(+,+)$, Quadrant II $(-,+)$, Quadrant III $(-,-)$, Quadrant IV $(+,-)$. For example, $\cos \frac{5\pi }{3}$ uses reference angle $\frac{\pi }{3}$ in Quadrant IV, so $\cos \frac{5\pi }{3}=\cos \frac{\pi }{3}=\frac{1}{2}$.