try

來源: 於 2015-02-09 16:02:41 [博客] [舊帖] [給我悄悄話] 本文已被閱讀：次

x^2+xy+y^2 = (z^3+y^3)/(x^2-xy+y^2)/3 + ... ,>= {(x+y)(y+z)(z+x)}^{1/3} (applying A-G inequality, simplify) , which is no less than 2 by A-G and xyz=1