Question

Determine the center and radius of the following circle equation:

Answer 1

Answer:

(6, 9 ) and r = 3

Step-by-step explanation:

The equation of a circle in standard form is

(x - h)² + (y - k)² = r²

where (h, k) are the coordinates of the centre and r is the radius

Given

x² + y² - 12x - 18y + 108 = 0

Rearrange the x- terms and the y- terms together and subtract 108 from both sides, that is

x² - 12x + y² - 18y = - 108

To obtain standard form use the method of completing the square

add ( half the coefficient of the x and y terms )² to both sides

x² + 2(- 6)x + 36 + y² + 2(- 9)y + 81 = - 108 + 36 + 81

(x - 6)² + (y - 9)² = 9 ← in standard form

with centre = (6, 9 ) and r = $\sqrt{9}$ = 3