Question

Which is the equation of a circle centered at the origin with radius 20?

Answer 1

x^2 + y^2 = 400

Explanation:

The equation for a circle is

(x-h)^2 + (y-k)^2 = r^2

where (h,k) is the center and r is the radius

(x-0)^2 + (y-0)^2 = 20^2

x^2 + y^2 = 400