学生在处理某些集合问题时，对学过的知识没有牢固掌握，不能灵活运用，常会产生一些意料之外的错误或走了弯路.为此，在集合问题的教学中必须培养学生“先思后虑”的良好习惯.1.“先思”由于集合，集合中的元素，集合的运算等有许多重要的性质和特征.如元素的确定性、互异性、 When students deal with certain sets of questions, they do not have a firm grasp of what they have learned, they cannot use them flexibly, and they often have some unexpected errors or detours. To do this, students must be trained in the teaching of collective problems. After thinking about “good habits.” “First think” because of the collection, the elements of the collection, the operation of the collection, etc. There are many important properties and characteristics, such as the certainty of the elements, heterogeneity,