Question

center (0,0); r= square root of 12

Answer 1

(4,5); r= square root of 12

Answer 2

Standard form of circle's equation is
(x-h)^2-(y-k)^2=r^2
where (h,k) are coordinates of the centre
and r is radius
(x-0)²+(y-k)²=√12²
x²+y²=12