Answer: x^2 + y^2 + 18y + 81 = 0
Explanation:
The equation of a circle with center at the point (0, -9) and radius 9 is given by the following equation:
(x - 0)^2 + (y + 9)^2 = 9^2
This can be simplified to the following:
x^2 + y^2 + 18y + 81 = 0
This is the equation of a circle with center at (0, -9) and radius 9.