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Question
Find centre and radius of the following circles
x2 + y2 + 6x – 4y + 4 = 0
Solution
x2 + y2 + 6x – 4y + 4 = 0
Comparing with the general form we get
2g = 6
2f = – 4
⇒ g = 3, /= – 2 and c = 4
Centre = (– g, – f)
= (– 3, 2)
Radius = `sqrt(g^2 + f^2 - "c")`
= `sqrt(9 + 4 - 4)`
= 3
∴ Centre = (– 3, 2) and radius = 3
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