General form of equation of circle (1),
(x-h)²+(y-k)²=r²....(1)
h=-f=0
k=-g=0
Cause centre is (-f,-g)or (h,k)
here centre is (0,0)
where r is the radius of the circle,
So the general form of equation o f a circle having centre (0,0) is ,
x²+y²=r²
or,x²+y²-r²=0
