Centre and radius of a circle

[Steve8112]

Plz help me.

Find the centre and radius of the circle

x^2+y^2-6x+4y-12=0.

[DaveD]

You need to get this in the form (x-a)^2 + (y-b)^2 = r^2
where the centre is (a,b) and radius=r

x^2 +y^2 -6x + 4y -12 = 0
x^2 +y^2 -6x + 4y =12
x^2 - 6x + y^2 + 4y = 12
Complete the square for the x's and the y's
(x-3)^2 - 9 +(y+2)^2 - 4 =12
(x-3)^2 + (y+2)^2 =12+9+4
(x-3)^2 + (y+2)^2 = 25

centre (3,-2) radius=5