(A-B)UB=A holds only when B is included in A. Under normal circumstances, only (A-B)UB=AUB and (A+B)UB=AUB can be obtained. Whether it can be further simplified depends on your other conditions.

(a-b) UB=AUB-BUB=(AUB)-B=A written by JK3Dym is completely wrong. (A-B)UB is not equal to AUB- Bubu, and (AUB)-B=A is only valid under certain conditions. Don't be misled.

Postgraduate entrance examination mathematics basic stage, thoroughly understand the textbook, master the outline.

Combine the undergraduate teaching materials with the previous year's syllabus, and thoroughly understand the basic concepts, methods and theorems. Mathematics is a deductive science with strong logic. Only by deeply understanding the basic concepts and firmly remembering the basic theorems and formulas.

In order to find the breakthrough and breakthrough point to solve the problem. The analysis of mathematics answer sheets in recent years shows that one of the important reasons why candidates lose marks is that they have incomplete memory of basic concepts and theorems, poor memory, inaccurate understanding and poor grasp of basic problem-solving methods.

The initial review of postgraduate entrance examination should lay a solid foundation in an all-round way and focus on making up for the weak links. Mathematics review for postgraduate entrance examination is basic and long-term, and it should be put in the first place in the initial stage of postgraduate entrance examination.

This is the way to review the basics of mathematics. Reading, doing problems and thinking are indispensable. Reading is the premise and foundation, and it is possible to do the right topic through reading. Doing the problem is the key and the purpose. Only by knowing how to do the questions, doing the right questions and doing the questions quickly can we cope with the exams and achieve our goals. Thinking is to read and do problems more effectively.