$(a,0)$ and $(b,0)$ are center of two circles belonging to a co-axial system of which y-axis is the radical axis. If radius of one of the circles is 'r', then the radius of the other circle is

Question

$$(a)\;(r^2+b^2+a^2)^{1/2}\quad (b)\;(r^2+b^2-a^2)^{1/2} \quad (c)\;(r^2+b^2-a^2)^{1/3} \quad (d)\;(r^2+b^2+a^2)^{1/3}$$