Find a pair of parametric equations whose graph is a circle

Find a pair of parametric equations whose graph is a circle centered at the origin with radius 3 such that:

a) the positive orientation is counterclockwise and the complete circle is sketched over the parameter interval 0 <_ t _< 1

b) the positive orientation is clockwise and the complete circle is sketched over the parameter interval 0 <_ t <_ (pi/2)

Center at (0,0)
radius = 3

a)
0 <= t <= 1

So, our normal circle equation in parametric is :
x = 3cost
y = 3sint
with 0 <= t <= 2pi

Now, we need to change to 0 <= t <= 1

So, write it as :
x = 3cos(2pi*t) , y = 3sin(2pi*t)
with 0 <= t <= 1

------------------------------------------------------------------

b)
Similarly, here we need
0 <= t <= pi/2

So, write that as :
x = 3cos(4t) , y = 3sin(4t)
with 0 <= t <= pi/2