## Precalculus (6th Edition) Blitzer

($\frac{1}{2}$ , -$\frac{\sqrt 3}{2}$) sec $\frac{5\pi}{3}$ is computed by $\frac{1}{x}$. So sec $\frac{5\pi}{3}$ = $\frac{1}{\frac{1}{2}}$ = 2.