a^2/b+b>=2ab^2/c+c>=2bc^2/a+a>=2c上面三式相加得a^2/b+b^2/c+c^2/a+a+b+c>=2(a+b+c)即 a^2/b+b^2/c+c^2/a >=a+b+c等号当且仅当a=b=c时成立
