If g2+f2=c, then the equation x2+y2+2gx+2fy+c=0 will represent
A circle of radius g
A circle of radius f
A circle of diameter √c
g2+f2−c (given), ∴ Radius = 0.
Which of the following equations represents a circle with centre (g,f) and radius √g2 + f2 + c ?