Given circles, x2+y2−4x−6y+12=0 If the equation of circle is x2+y2+2gx+2fy+c=0 ∴c=(−g1−f) and r=√g2+f2−c Centre C1(2,3) and radius r1=1 and x2+y2+4x−2y−4=0 Centre C2(−2,1) and radius r2=3 Co-ordinate of internal centre of similitude of circles =(