Answer:
here ,
origin means (0,0)
so ,
h and k are 0 and 0
and diameter ( d) is 4
r = d/2
using formula
(x-h)^2 +( y-k)^2 = r^2
(x-0)^2 +( y-0)^2= 2^2
x^2+y^2= 4 is the equation.
