解答排列组合问题的关键是要不重复不遗漏,要做到不重不漏,的确比较困难,有时重复和遗漏的情况不易察觉.一道高考题,笔者计划十分钟讲完,学生出现了一些错误思路,我认为:如果不帮助他们分析清楚,找出错因,他们还会犯同样的错误.为此我调整教学计划,逐一分析学生的典型错误,并由 The key to solving the problem of permutation and combination is not to repeat it. It is indeed more difficult to do it, and sometimes it is difficult to perceive the situation of repetition and omission. With a college entrance examination question, the author planned to finish it in ten minutes, and the student has made some mistakes. Thinking, I think: If you don’t help them analyze clearly and look for the wrong reasons, they will make the same mistakes. To this end, I adjust the teaching plan and analyze each student’s typical mistakes one by one.