1. There is no very important formula to master completely, but the basic skills of solving equations are good, and quadratic inequalities should be understood.

2. It means that the combination of the elements in A and B is R, and the expression of the number axis means that the whole number axis is within the range.

3. Union, for example, A∪B is the sum of elements in A and B (note that elements are not repeated). If A = (1, 2,3) b = (1,2,4), A ∪ B = (1, 4).

4.or means union, that is, at least one of the conditions is met.

5. proper subset refers to a subset other than itself. An empty set is the proper subset of all non-empty sets. The number of computing subsets is 2 n, and the number of proper subset is 2 n- 1. The main difference is that subsets contain themselves.