A complete set is a relative concept, which only contains all the elements involved in the studied problem, and a complementary set is only relative to the corresponding complete set. For example, when we study the problem in the integer range, Z is a complete set, and when the problem is extended to the real number set, R is a complete set, and the complementary set is only relative to this.
Extended data
Complement set is not only the relationship between sets, but also the operation between sets. The premise of finding the complement of set A is that A is a subset of complete set U, and the obtained complement is different with the different complete sets selected, so it is two concepts that are interdependent and inseparable.
UA has three meanings: ①A? u； ②? UA is a set, and? UA？ u； ③? UA is a set of all elements in U that do not belong to A..
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