Respuesta :

Answer: r = 2

Step-by-step explanation: The general equation is:

(x-a)² + (y-b)² = r²

where (a,b) = coordinates of the center, and r = radius

x² + y² = 4 is the same as

(x-0)² + (y-0)² = 2²

So, the center is at (0,0) and the radius is 2.