Find $t$ for the following terminal points:
(a) $P(0,1)$, $t=$ ;
(b) $P(-\frac{\sqrt{2}}{2},\frac{\sqrt{2}}{2})$, $t=$ ;
(c) $P(-1,0)$, $t=$ ;
(d) $P(-\frac{\sqrt{2}}{2},-\frac{\sqrt{2}}{2})$, $t=$ ;
(e) $P(0,-1)$, $t=$ ;
(f) $P(\frac{\sqrt{2}}{2},-\frac{\sqrt{2}}{2})$, $t=$ .