(b) The radical axis of any two circles is perpendicular to the line joining their centres. Let, the equation of two circles are x2+y2+2g1x+2f1y+c1=0 and x2+y2+2g2x+2f2y+c2=0 The equation of the radical axis is 2(g1−g2)x+2(f1−f2)y+(c1−c2)=0.....(i) ∵ Slope of line (i) is −
g1−g2
f1−f2
=m1......let(ii) and slope line joining centres of the circles is