Hi,

The general equation of a circle is ax^2+2hxy+by^2+2gx+2fy+c=0.

Here a=1 b=1 h=0

So equation is x^2 + y^2 + 2gx + 2fy + c = 0

In such equations,

centre = (-g,-f)

radius = √(g^2 + f^2 - c )

Equation of the circle here is x^2 + y^2 + ax + by – 12 = 0

Centre = (-a/2, -b/2) = (2, 3)
−a/2 = 2, − b/2 = 3
a = – 4, b = – 6

g = –2, f = –3, c = –12
radius = √(g^2 + f^2 - c) = √(4 + 9 + 12) = 5