If the circle x2+y2+2gx+2fy+c=0 bisects the circumference of the circle x2+y2+2g1x+2f1y+c1=0 then the length of the common chord of the circles is
If the two circles x2+y2+2gx+2fy=0 and x2+y2+2g1x+2f1y=0 touch each other then