Union: symbol ∨, which means to take all elements of two sets. Memory method: the symbol of closure is the inverted door.
for instance
The intersection of (1) set {1, 2,3} and {2,3,4} is {2,3}. That is {1, 2,3} ∩ {2,3,4} = {2,3}.
(2) The number 9 does not belong to the prime set {2, 3, 5, 7,1,...} and the odd set {1, 3, 5, 7, 9,1,...} {x|x is prime }∩{x|x is odd}.
The union of sets {1, 2,3} and {2,3,4} is {1, 2,3,4}. The number 9 does not belong to the union of the prime set {2, 3, 5, 7, 1 1, …} and the even set {2, 4, 6, 8, 10, …}, because 9 is neither prime nor even.
Extended data:
Binary union (union of two sets) is a combination operation, that is, A ∨( B∪C)=(A∪B)∪C, in fact, A∪B∪C is also equal to these two sets, so parentheses can be omitted when only union operation is performed. Similarly, the union operation satisfies the commutative law, that is, the order of the sets is arbitrary.
Empty set is the unit element of union operation. Namely. ∪A=A = A. For any set A, an empty set can be regarded as the union of zero sets.
References:
Baidu encyclopedia-collection