For the given values of an angle $\alpha$, find the terminal point $P(x,y)$ on the unit circle.

(a) If $\alpha=\frac{\pi}{2}$, then $x=$ and $y=$ ;

(b) If $\alpha=-\frac{\pi}{2}$, then $x=$ and $y=$ ;

(c) If $\alpha=\frac{\pi}{3}$, then $x=$ and $y=$ ;

(d) If $\alpha=-\frac{\pi}{3}$, then $x=$ and $y=$ ;

(e) If $\alpha=\frac{3\pi}{4}$, then $x=$ and $y=$ ;

(f) If $\alpha=-\frac{3\pi}{4}$, then $x=$ and $y=$ ;

Hint: