Okay I'm having trouble parameterizing the curve C: x^2 + y^2 = 4 from (0,2) to (SQRT 2, SQRT 2) in the first quadrant in order to take the line integral for f (x,y) = x^2-y

I understand to put C into polar coordinates, and that r=2 but my key shows that r(t) = (2cost)i + (2sint)j 0<=t=<pi/2

and I have no idea how to get that r(t)...