Centre of circle cuts the circles S1:x2+y2+4x+3=0 S2:x2+y2−12x+35=0 Radical Axis is S1−S2=0⇒x=2 and (2,0) lies on the line segment joining centres of circles S1 and S2 Minimum radius = length of tangent from (2,0) to circle S1=0 (or) S2=0 =√4+8+3=√15