∩: intersection. For example, A∩B represents the set of all elements in set A and set B.

∈: belongs to. For example, a∈A means that element A belongs to set A.

X( 123)B( 12)X∩BX intersection b is equal to (12).

X( 123)B( 12)B∈XB belongs to X and is equal to (12).

X( 123)B( 12)X∪BX and b are equal to (123).

Extended data:

classify

null set

There is a special set that does not contain any elements, such as {x|x∈Rx? +1=0} is called an empty set, remember? . An empty set is a special set, which has two characteristics:

Empty set? Is any non-empty set of proper subset.

An empty set is a subset of any set? [4]?

subset

Let s and t be two groups. If all the elements of S belong to T, then S is a subset of T, and denoted as. Obviously, for any set s, there is. ?

Among them, the symbol? When read as containing, it means that all elements in the set on the left side of the symbol are elements in the set on the right side of the symbol. If S is a subset of T, that is, but there is an element X in T that does not belong to S, that is, S is the proper subset of T?

Intersection and union

Intersection definition: a set consisting of the same elements belonging to A and B, marked as A∩B (or B∩A), which is pronounced as "A intersects with B" (or "B intersects with A"), that is, A∩B={x|x∈A, and x∈B} Note that the intersection is getting less and less. If a contains b, then A∩B=B, A∪B=A? [5]。

Union definition: A set consisting of all elements belonging to set A or set B, marked as A∪B (or B∪A), pronounced as A and B (or B and A), that is, A∪B={x|x∈A, or X ∈ B. Pay more attention to union, which is intersection. [5]。

supplementary set

Complement sets can be divided into relative complement sets and absolute complement sets.

Definition of relative complement set: A set composed of elements belonging to A but not to B, called B's relative complement set about A, and denoted as A-B or A\B, that is, A-B={x|x∈A, and X? B'}[5].

Definition of absolute complement set: A's relative complement set about complete set U is called A's absolute complement set, and it is denoted as A' or? U(A) or ~ a. There is u' = φ; φ' = U

References:

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