Two circles x2+y2+2gx+c=0x^2 + y^2 + 2gx + c = 0x2+y2+2gx+c=0 and x2+y2+2fy+c=0x^2 + y^2 + 2fy + c = 0x2+y2+2fy+c=0 touch each other. What is the condition on g,f,cg, f, cg,f,c?
c2=g2f2c^2 = g^2f^2c2=g2f2
1/c=1/g2+1/f21/c = 1/g^2 + 1/f^21/c=1/g2+1/f2
c=gfc = gfc=gf
g2+f2=c2g^2 + f^2 = c^2g2+f2=c2