P is arrangement: (People's Education Edition writes P as a) For example, if you choose two arrangements from ABC, then AB and BA are two combinations, and there are six arrangements: AB BA AC, CA, BC and CB.
From n different elements, any m(m≤n, m, n is a natural number) elements are arranged in a row in a certain order, which is called the arrangement of taking out m elements from n different elements; All permutation numbers of m(m≤n) elements taken from n different elements are called permutation numbers of m elements taken from n different elements, which are denoted by symbol A(n, m) and denoted by P(n, m) in old textbooks.
Extended data:
Addition principle: There are n ways to do something. Finish it. The first way, there are m 1 different ways, the second way, there are m2 different ways, …, the nth way, there are mn different ways, so there are N=m 1+m2+m3+…+mn different ways to complete it.
The method of the first method belongs to the set A 1, the method of the second method belongs to the set A2, ..., And the method of the n method belongs to the set an, so the method to accomplish this belongs to the set A 1ua2u...uan.
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