1.本单元重点、难点分析本单元的重点:两个计数原理,排列、组合的定义,排列数、组合数的定义以及排列数、组合数的公式,组合数的性质;二项式定理,二项展开式的通项.本单元的难点:复合事件的分类与分步,含有限制条件的排列组合应用问题;二项展开式的通项的灵活运用.学习排列、组 1. The focus of this unit is to analyze the key points of this unit: the two counting principles, the definition of arrangement, combination, the number of arrays, the definition of the number of combinations, the formula of the number of arrays, the number of combinations, and the nature of the number of combinations; binomial theorem, The general term of the binomial expansion. Difficulties in this unit: classification and stepping of complex events, application of permutations and combinations with constraints, and flexible use of binomial generalizations. Learning arrangements, groups