Answer
$\{0^{o}, \ \ 180^{o}\}$
Work Step by Step
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: $\{0^{o}, \ \ 180^{o}\}$
