A) Find the center-radius form of the equation of the circle with center (0,0) and radius 18.

Step-by-step explanation:

Center-radius equation for circle of radius r, centered at (h,k):

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

x^2 + y^2 = 18^2

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.