Answer:
4
Step-by-step explanation:
We can write the equation of a circle as
(x-h)^2 + (y-k)^2 = r^2
where (h,k) is the center and r is the radius
x^2 + y^2 = 16
can be rewritten as
(x-0)^2 + (y-0)^2 = 4^2
Where the center is (0,0) and the radius is 4
