General equation of a circle (x²+y²+2gx+2fy+c=0)

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x²+y²+2gx+2fy+c=0

What each symbol means

Symbol	What it stands for
r	$\sqrt{g^2+f^2-c}$
g,f,c	Constants
center	(-g,-f)

When to use this

g²+f²−c>0 for real circle.