Find the equation of the circle with centre $(0,2)$ and radius $2$.

Question

$\begin{array}{1 1} x^2+y^2-4y=0 \\ x^2+y^2+4y=0 \\x^2+y^2+4y-4=0 \\x^2+y^2-4y+4=0\end{array} $