collection classification:

union: a set with elements belonging to a or b as elements is called the union (set) of a and b, denoted as a∪b (or b∪a), and pronounced as "a and b" (or "b and b"). a"), that is, a∪b={x|x∈a, or x∈b}

for example, the complete set u={1, 2, 3, 4, 5} a={1, 3, 5} b={1, 2, 5}.

their two sets contain five elements, 1, 2, 3, 4, and 5, regardless of the number of times the element appears, as long as the element appears in these two sets. then say a∪b={1, 2, 3, 5}. the shaded part in the figure is a∩b.

intersection: a set with elements belonging to a and b as elements is called the intersection (set) of a and b, denoted as a∩b (or b∩a), and pronounced as "a intersects b" (or "b intersects a"). ”), that is, a∩b={x|x∈a, and x∈b}

for example, the complete set u={1, 2, 3, 4, 5} a={1, 3, 5} b={1, 2, 5}. then because there are 1,5 in a and b, a∩b={1,5}.

difference: a set whose elements belong to a but not to b is called the difference (set) between a and b.