证明：∵（x-y)^2(x+y)≥0∴(x-y)(x^2-y^2)≥0∴x^3+y^3≥x^2y+xy^2同理x^3+z^3≥x^2z+xz^2z^3+y^3≥z^2y+zy^2xyz不都相等,所以上面三式不能同时取等号∴x^3+y^3+x^3+z^3+z^3+y^3>x^2y+xy^2+x^2z+xz^2+z^2y+zy^2 ∴2...