Through some numbers, at some time, some people, some Zheng's, some objects, including some people, put all the objects in each group together, or put some designated objects together as a set called the set of elements in each group.
Definition: Generally speaking, a set of specified objects becomes a set. We 1, concept
Set (1) Set: Gather some specific objects together to form a set (short set). Day (2) Content: Each object in the set is called the element of the set br >；; 2. Set and universal symbol days (1) Non-negative integers (natural numbers): When all non-negative integers are expressed as n, odd and even positive integer sets (2): 0 non-negative integer sets are excluded as N * or N+.
Biso (3) integer set: all the integers Z in the heart, the set set reasonably set by day (4): let all rational numbers be q,
(5) Real number set: R recorded in the whole real number set.
Note: (1) The set of natural numbers is the same as non-negative integers, that is, the number of natural number sets includes
0 days (2) Exclude 0 groups of records and exclude other records.
If the number of the set N * or N+Q, z and r is 0, if it is a non-negative integer, it is also said, such as excluding the integer 0.
Set, expressed as Z * Page 3, membership degree of elements.
The set (1) is: If A is an element of the set A, for example, a part of A, it is recorded as A ∈ A.
(2) Does not belong to: If A belongs to the element A in the set, it is said that it does not belong to A and recorded as.
4. Collect features
Element (1) uncertainty: an element is given or assembled according to a clear standard here, and whether it is second-hand or not cannot be ambiguous. (2) Diurnal variation: the assembly of elements does not repeat pesos. (3) Diseases: Not necessarily in order (usually written in normal order) Page 5. (1) Assembly is usually capitalized in Latin letters, such as a collection of elements A, B and C. ......
Components are usually represented by lowercase Latin letters, such as a, b, c, p and q. ......
(2) "∈" is the opening direction, and a∈A cannot be reversed.
Three tasks: we 1, P5 textbook exercise 1, 2.
2. Which of the following object groups can determine a group? Peso (1) All great real (uncertain) days (2) Good people (uncertain) peso (3) 1, 2, 2, 3, 4, 5. (Repeat), page 3, let A and B be the constituent elements of a non-zero real number set, then this value may need _-2, 0, 2__.
4. Real numbers x, -x, | X | form a group, which contains at most (1) days (A)2 elements (B)3 elements (c) 4 elements (D)5 yuan Page 5, as long as A+B(a∈Z, b∈Z) is concentrated.
(1) When x∈N times, x ∈ g;
(2) if x∈G, y∈G, then X+Y∈G, but not necessarily belong to the set g.
Proof (1): A+B (A ∈ Z, b∈Z), so A =x∈N, B = 0, second-hand X = X+0 * = A+B∈G, that is, x ∈ g.
Proof (2):∫x∈G, y∈ G,
∴x= A + B(a∈Z，b∈Z)，Y = C + D(c∈Z，d∈Z)
∴x+ Y =(A + B)+( C + D)=(A + C)+(B + D)
∫a∈Z，b∈Z，c∈Z，d∈Z
∴(A + C)∈Z，(B + D)∈Z
∴x+ Y =(A+C)+(B+D)∈G, second-hand also ∵ = Asian sum need not be an integer, and second-hand ∴ = does not necessarily belong to the set g.