2. In any given set, any two elements are different objects. When the same object is contained in a collection, it is only an element. ?
3. The elements in the set are equal, and there is no order. Therefore, to judge whether two sets are the same, it is only necessary to compare whether their elements are the same, and it is not necessary to check whether the arrangement order is the same. ?
4. let the quadratic function y = x 2 be the image in the plane rectangular coordinate system. It can be seen that the image of quadratic function is a parabola.
5. The three characteristics of set elements make the set itself deterministic and holistic.