# Math Help - Circle Problems

1. ## Circle Problems

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,

2. They're both correct.

3. ok, well thats a relief that myne is correct, can you possibly explain to me how thiers works?

As it was required to evaluate a double integral, and i seem to have trouble understanding the way they have gone about it,

Many thanks

4. Originally Posted by monster
ok, well thats a relief that myne is correct, can you possibly explain to me how thiers works?

As it was required to evaluate a double integral, and i seem to have trouble understanding the way they have gone about it,

Many thanks
$\big(-2 \sin(0), 2 \cos(0)\big) = (0,2) = \big(2\cos(\pi /2), 2\sin(\pi/2)\big)$

$\big(-2 \sin(\pi /2), 2 \cos(\pi /2)\big) = (-2,0) = \big(2\cos(\pi), 2\sin(\pi)\big)$

It doesn't matter which parametrization you use.