百度知道。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设x^3=a,y^3=b,z^3=c则:a+b+c)/3≥三次根号(abc)推广到n也成立但一定要记住,前提是:a,b,c是非负数---
