Hello, I want to apply green's theorem to:

$\displaystyle \int_C 2xds$ where $\displaystyle C$ is the line that delimit a circle centered in $\displaystyle (0,0)$ with radius=1

green's theorem says:

$\displaystyle \int_C (f(x,y)dx + g(x,y)dy)= (...)$

So, how can I apply it?

Thank you!