Answer: x^2 + y^2 - 4x + 18y = 76 = 0
The center of the circle given is (2, 9)
radius = r
The equation of a circle for a given point is
(x - h)^2 + (y - k)^2 = r^2
Where h = 2, and y = 9
(x - 2)^2 + (y - 9)^2 = 3^2
Expand the parentheses
(x - 2) (x - 2) + (y - 9) (y - 9) = 9
(x - 2) (x - 2 ) = x* x - 2*x - 2*x + 2* 2
= x^2 - 4x + 4
(x - 2) (x - 2) = x^2 - 4x + 4
(y - 9) (y - 9) = y*y - y*9 - 9*y + 9*9
= y^2 - 18y + 81
(y - 9) (y - 9)= y^2 - 18y + 81
Therefore, the equation becomes
x^2 - 4x + 4 + y^2 - 18y + 81 = 9
Re-arrange the equation
x^2 + y^2 - 4x - 18y + 4 + 81 = 9
x^2 + y^2 - 4x - 18y = 9 - 81 - 4
x^2 + y^2 - 4x - 18y = -76
x^2 + y^2 - 4x - 18y + 76 = 0
The equation of a circle given the center (2, 9) and radius 3 is x^2 + y^2 - 4x + 18y = 76 = 0