Question

What is the center and radius of the circle with the equation x2 + y2 + 8x – 12y + 36 = 0 ?
Center: (5, 6); Radius = 4
Center: (–4, 6); Radius = 5
Center: (5, 6); Radius = 5
Center: (–4, 6); Radius = 4

Answer 1

complete the square for x and y

x^2 + 8x + y^2 - 12y = -36

x^2 + 8x + 16 + y^2 - 12y + 36 = -36 + 36 + 16

factorising

(x +4)^2 +(y -6)^2 = 4^2

the centre is (-4, 6) radius 4

Answer 2

the general form of a circle is

(x - h)^2 + (y - k)^2 = r^2

centre (h, k) radius = r

Answer 3

Thanks (: