The general equation of a circle is given by;
\((x-a)^{2} + (y-b)^{2} = r^{2}\)
Where (a, b) is the centre of the circle and r is the radius.
For the given circle, centre is (0,0) and r=9
This
\((x-0)^{2} + (y-0)^{2} = 9^{2}\)
\(x^{2} + y^{2} = 9^{2}\)
