“要仔细，勿粗心”是老师经常告诫学生的话．但是，任何事情都有“度”，过度的“细”会使人专注于细微末节，培养不出从整体上把握问题的能力和高屋建领的解题气势．所以，对有些问题不妨适度地“粗”一点．例呈设集合A一｛a，a‘，ah｝，B一门，a，b｝，且A—B，求实数a和b “Be careful and not careless” is what the teacher often tells the students. However, everything has “degrees”. Excessive “fineness” can lead people to focus on the subtleties of the details, and they cannot cultivate the ability to grasp the problems as a whole and the problem-solving power of high-house construction. Therefore, some problems may be moderately “coarse”. The example assumes that the set A-{a, a’, ah}, B-gate, a, b}, and A-B, the real numbers a and b