√(x^2+xy+y^2)+√(y^2+yz+z^2)+√(z^2+zx+x^2)
>=√(1/4*x^2+xy+y^2)+√(1/4*y^2+yz+z^2)+√(1/4*z^2+zx+x^2)
=√(1/2*x+y)^2+√(1/2*y+z)^2+√(1/2*z+x)^2
=1/2*x+y+1/2*y+z+1/2*z+x
=(3/2)(x+y+z)