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1.对于特殊元素与特殊位置的优先考虑对于具有特殊元素或者特殊位置存在的排列组合问题,应当首先符合特殊元素或者特殊位置的具体要求,再分析其余元素或者位置的问题.例题1一位教师与四位学生排队站成一排进行照相,如果教师不允许站在队伍的两端位置,则总共可以由多少种不同的排列方法?解法1(特殊元素法):教师站在队伍中间的三个具体位置上任意选择一个位置的选择方法有A_3~1种情况.然
1. Prioritisation of Special Elements and Special Locations For arrangements with special elements or special locations that exist, you should first meet specific requirements for specific elements or special locations, and then analyze the remaining elements or locations. Example 1 A teacher With four students lined up to photograph in a row, if the teacher is not allowed to stand at both ends of the team, how many different arrangements can be total? Solution 1 (special element method): The teacher stands in the middle of the team three There are A_3~1 cases for the selection method of arbitrarily selecting a location on a specific location.