The general equation of a circle in form $x^2 + y^2 + 2gx + 2fy + c = 0$ has centre and radius:
Acentre $(-g, -f)$, radius $\sqrt{g^2 + f^2 - c}$
Bcentre $(g, f)$, radius $\sqrt{g^2 + f^2 - c}$
Ccentre $(-g, -f)$, radius $\sqrt{c}$
Dcentre $(g, f)$, radius $c$
Answer & Solution
Correct answer: A. centre $(-g, -f)$, radius $\sqrt{g^2 + f^2 - c}$
Completing squares: centre $(-g, -f)$ and $r = \sqrt{g^2 + f^2 - c}$.
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