设a=x^3,b=y^3,c=z^3 x,y,z是非负数时 x^3+y^3+z^3-3xyz =(x+y+z)(x^2+y^2+z^2-xy-yz-xz) =(x+y+z)[(x-y)^2+(y-z)^2+(x-z)^2]/2≥0 所以,x^3+y^3+z^3≥3xyz 则:(a+b+c)/3≥三次根号(abc)