#### Answer

The answer is $c(t)=(2\cos(t+\frac{\pi}{3}),2\sin(t+\frac{\pi}{3})$.

#### Work Step by Step

This is the equation of the circle of radius 2 centered at the origin. The parametrization is given by $c(t)=(2\cos t,2\sin t)$.
At $t=0$, we have $(x(0),y(0))=(1,\sqrt{3})$.
So, we may take $x(t)=2\cos(t+\frac{\pi}{3})$. So, $y(t)=2\sin(t+\frac{\pi}{3})$.
Thus, the parametrization of $x^2+y^2=4$ is $c(t)=(2\cos(t+\frac{\pi}{3}),2\sin(t+\frac{\pi}{3})$ for $0\leq t\leq 2 \pi$.