C(m, n)m is at the bottom and n is at the top, which means that N elements are selected from M elements for combination.
Calculation of c: the number of subscripts is multiplied by the number of tags, and each digit must be-1. Then divide by the factorial of the marked number.
For example: C5 3 (subscript 5, superscript 3)=(5X4X3)/3X2X 1.
3X2X 1 (i.e. factorial of 3)
Calculation of a:
Just like the first step of C, there is no need to divide the factorial of the above target.
For example A4 2 = 4X3.
Definition of extended data arrangement: from n different elements, any m(m≤n, m and n are natural numbers, the same below) elements are arranged in a certain order, which is called the arrangement of m elements in 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 represented by symbol A(n, m).
Definition of combination: taking any m(m≤n) elements from n different elements to form a group is called taking the combination of m elements from n different elements; The number of all combinations of m(m≤n) elements from n different elements is called the number of combinations of m elements from n different elements. Represented by the symbol C(n, m).