A circle x2+y2+2gx+2fy+c=0x^2 + y^2 + 2gx + 2fy + c = 0x2+y2+2gx+2fy+c=0 touches the xxx-axis if:
g2=cg^2 = cg2=c
f2=cf^2 = cf2=c
g2+f2=cg^2 + f^2 = cg2+f2=c
c=0c=0c=0