Find the terminal point $P(x,y)$ on the unit circle determined by the given value of $t$:
(a) If $t=\frac{\pi}{2}$, then $x=$ and $y=$ ;
(b) If $t=-\frac{\pi}{2}$, then $x=$ and $y=$ ;
(c) If $t=\frac{\pi}{3}$, then $x=$ and $y=$ ;
(d) If $t=-\frac{\pi}{3}$, then $x=$ and $y=$ ;
(e) If $t=\frac{3\pi}{4}$, then $x=$ and $y=$ ;
(f) If $t=-\frac{3\pi}{4}$, then $x=$ and $y=$ ;