在近几年的试卷和参考书中 ,出现了一类以否定形式叙述的命题 .这些试题具有一定的深度 ,设计别出心裁 ,具有较强的选拔性 ,直接解答或证明有一定的困难 .解此类题目常见的方法有以下几种 .一、利用命题之间的关系例 1　证明“若a2 + 2ab+b2 +a+b-2 ≠ 0 ,则a +b≠ 1”为真命题 In the examination papers and reference books of recent years, there have appeared a series of propositions in the form of negation. These questions have a certain depth, the design is ingenious, has a strong selection, and it directly answers or proves that there are certain difficulties. The common methods of class topics are the following. First, use the relationship between propositions Example 1 Prove “If a2 + 2ab + b2 + a + b-2 ≠ 0, then a + b ≠ 1” is a true proposition