证明：运用公式：A^3+B^3+C^3>=3ABC a/x+b/y+c/z>=3(a/x)^(1/3)(b/y)^(1/3)(c/z)^(1/3) =3(abc/xyz)^(1/3) =3(abc/abc)^(1/3) =3 所以,a/x+b/y+c/z>=3
