[tex] x^2 + y^2 - 4x + 2y - 11 = 0 [/tex]
You need to complete the square for both x and y.
[tex] x^2 - 4x + y^2 + 2y = 11 [/tex]
[tex] x^2 - 4x + 4 + y^2 + 2y + 1 = 11 + 4 + 1 [/tex]
[tex] (x - 2)^2 + (y + 1)^2 = 16 [/tex]
[tex] (x - 2)^2 + (y + 1)^2 = 4^2 [/tex]
The center is (2, -1).
The radius is 4.
