Combination is one of the important concepts in mathematics, which refers to taking out m different elements from n different elements at a time, regardless of their order, and synthesizing a group, which is called the combination of selecting m elements from n elements without repetition. The number of species in all such combinations is called the combination number.

The combination obtained by repeatedly extracting m elements from N-ary set A is essentially the sum of M-ary subsets of A. If ordered set A becomes an ordered set, then the combination of M elements extracted from A corresponds to some strict order-preserving mapping from several fragments to ordered set A. ..

Tips for learning mathematics

1, you should be good at thinking when learning mathematics, and the answers you come up with are far more impressive than those others say.

2. Prepare well before class, so that we can better digest and absorb the unknown knowledge points in math class.

3, the mathematical formula must be memorized, and it must be deduced and can be deduced.

4. The most basic thing to learn mathematics well is to master the knowledge points of textbooks and exercises after class.