The elements in a set have three characteristics: disorder, mutual difference and certainty. Mutual difference means that the elements in the same set are different, such as {a, b, a}, which means that the set is incorrect. Because the elements in the set are repeated, the correct notation is (a, b); Determinism means that the relationship between an element and a set is very clear, either the element belongs to the set or the element does not belong to the set. For example, the relationship between element 6 and sets A = (1, 4) and B = (3, 4, 5, 6) is 6∈a and 6∈b, respectively. Disorder means that the elements in a set are out of order. For example, (1, 2,3) and (2, 1, 3) represent the same set.

2. Accurately grasp the representation of the set.

For beginners, the most difficult thing is how to express the set properly. In particular, the method x∈p) is described, where X is the research object and the elements X in the P-foot set have the same * * * attribute. First of all, we should find the research object, and then consider the commonness of X. For example, a=(x/y=x), the research object of A is X, the meaning of A is the range of independent variables in the function y-x. a = r, and the research object of B set is Y, and the meaning of B set is formed by the function Y = X. Corresponding to the ordinate of all points on the parabola. Generally speaking, the same set may have different representations, but infinite sets cannot be enumerated.

3. Pay attention to distinguish some confusing symbols.

(1) The difference between "∈" and "":"∈" is a symbol indicating the relationship between elements and sets, that is, the relationship between individuals and collectives, such as 2∈n, 2 ≠ n; A symbol indicating the relationship between sets, that is, the relationship between sets, such as n Ф r, Ф r.

(2) the difference between "A" and "A": "a b" includes "a b" and "a=0", and they must be one of them.

(3) The difference between (0) and Ф: {0} is a set of zeros with one element, and it is a set that does not give up any elements.

(4) such as the difference between {a} and a; {a} means a set with only one element, and A means one element.

To correctly understand the concept of subset, we can't say that subset is a set composed of some elements in the original set, otherwise it will be easily ignored when considering the subset of the set.