## Precalculus (6th Edition)

$\{0^{o}, \ \ 180^{o}\}$
For a point on the unit circle, the coordinates are ($\cos\theta,\sin\theta)$, $x\in[0^{o},360^{o})$ To solve the problem, find the points for which the $y$-coordinate is $0$, ($\sin\theta$=$0$) Using the given unit circle, we find such points (1,0), $\quad$for $x=0^{o}$ $(-1,0),\ \quad$for $x=180^{o}$ Solution set: $\{0^{o}, \ \ 180^{o}\}$