Question

Find the center and radius of the circle with this equation x^2+y^2+4x+2y+3=0

Answer 1

 general equation of a circle is $x^{2} + y^{2} +2gx+2fy+c = 0$
comparing with general equation we get 
g = 2; f =1; c =3
therefore centre is (g,f) = (2,1)
radius is$\sqrt{ g^{2} + f^{2} -c$
$= \sqrt{4+1-3}$
=$\sqrt{2}$