在竞赛数学中 ,新题的产生能体现出人类智慧的光辉 ;在历届竞赛数学的考试中总能涌现出许多耐人寻味的好题 ;本人就美国大学生竞赛中一道不等式试题进行研究时产生了很多想法 ,便提笔写了下来 ,共与喜好竞赛数学的读者一同分享 .题目　给定正实数a ,b,c,d .证明a3+b3+c3a +b +c In the competition mathematics, the emergence of new questions can reflect the brilliance of human wisdom; many intriguing good questions can always emerge in the examinations of previous competition mathematics; I have a lot of ideas when I study on an inequality test in the American college student competition. , wrote a pen, wrote a total share with the readers of the mathematics of mathematics. title given a positive real number a, b, c, d. prove a3 + b3 + c3a + b + c