Standard Equation of circle whose center is not at origin (0, 0):
(x - h)² + (y-k)² = r²
where (h,k) = center of the circle
r = radius (If diameter is given, divide it by two to get the radius.)
Radius: 18/2 = 9 units
Center: (h, k) = (-3, 8) h= -3 k= 8
Solution:
(x - -3)² + (y - 8)² = 9²
(x+3)² + (y-8)² = 81 Standard Form
General Form: x² + y² + Cx + Dy + E = 0
(x+3)² + (y-8)² = 81
x² + 6x + 9 + y² - 16y + 64 = 81
x² + y² + 6x -16y + 9 + 64 = 81
x² + y² + 6x - 16y + 73 - 81 = 0
x² + y² + 6x - 16y - 8 = 0
Standard Form: (x + 3)² + (y - 8)² = 81
General Form: x² + y² + 6x - 16y -8= 0