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

x^2 + y^2 = 400

Step-by-step 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

a complex number is a number that can be expressed in the form a + bi, where a and b are real numbers, and i is a solution of the equation x2 = −1. because no real number satisfies this equation, i is called an imaginary number. has no real solution, since the square of a real number cannot be negative.