Let the equation of circle be x2+y2+2gx+2fy+c=0 since, it passes through the point (2a,0), so 4a2+4ag+c=0 ...(i) Also, its radical axis with x2+y2=a2 is 2ax+2fy+c+a2=0 But the radical axis is x=
a
2
, so we get or
2g
1
=
c+a
−a∕2
and f=0 or ag+c+a=0 ...(ii) From Eqs. (i) and (ii), we get g and c Hence, the equation is x2+y2−2ax=0