The equation of any circle passing through the origin and with its centre on the $X$-axis is given by
Can you please checkout this.
I have doubt between options $a$ and $b$.
'a' can be negative, right ? Coordinates of centre can be (3,0) or (-3,0). Then equation will be $x^2 + y^2 + 6x =0 $ (or) $x^2 + y^2 - 6x =0 $ and In both cases, it will satisfy the given condition. right ?