Let be an angle such that is the terminal point of :

Let $x$ be an angle such that $P$ is the terminal point of $x$:

Some of the points $Q, R, S, T$ can be the terminal points of $\frac{x}{2}$. What are these points? 

And there is also a second part of this question, if someone can solve this too it would be very helpful (although I am very close to finishing).

Assume that $\cos(\theta/2) < 0$. Then if $\[\text{Terminal point of } \frac{\theta}{2} = (a_1, a_2),\]$, what is $a_1$ and $a_2$?