在高三数学复习中,有一道求映射个数题,题目如下: 已知A={1,2,3,4,5},B={6,7,8},从集合A到集合B的映射中,满足f(1)≤f(2)≤f(3)≤f(4)≤f(5)的映射有多少个? 通常的解法是:根据A中的元素在B中对应的元素个数分类.第1类,A中的元素对应B中的同一个元素,有C31=3个映射;第2类,A中的元素对应B中的两个元素,这里需要先确定是哪两个元素,所以要选出这两个元 In the third year mathematics review, there is a map number question, the title is as follows: Known A={1,2,3,4,5}, B={6,7,8}, from set A to set B In the mapping, how many maps satisfy f(1) ≤ f(2) ≤ f(3) ≤ f(4) ≤ f(5)? The usual solution is: According to the elements in A, the corresponding elements in B Number classification. In the first category, the elements in A correspond to the same element in B, and there are C31=3 mappings. In the second category, the elements in A correspond to the two elements in B. Here we need to determine which two Elements, so choose these two elements