I seem to keep having trouble with parameterizations of circles, particularly thier direction i think,

for instance for the quarter circle that goes anticlockwise from (0,2) to (-2,0) can someone explain to me how the parameterization is,

c(t)= (-2sint , 2 cost)

0 <= t<= pi/2

I would have thought;

x= rcost, y=rsint

Therefore; c(t) = (2cost, 2sint)

where pi/2 <= t <= pi

Any explanation would be very helpful,

Cheers,