A circle is a set of points in a plane equidistant
from a fixed point. It has a general formula of x² + y² = r². This is if the
center is at the origin. However, if the center at point h and k, the
equation becomes (x-h)² + (y-k)² = r².
We write the given equation in the
form (x-h)² + (y-k)² = r² by completing the square.
x²
+ y²
+ 10x – 6y + 18 = 0
(x² + 10x + 25 )+ (y² - 6y + 9) = −18 + 25 + 9 = 16
(x + 5)² + (y + 3)² = (4)²
Therefore,
center = (-5, -5)
radius = 4
