一注意集合元素的属性用描述法表示集合的一般形式为:{(?)具有公共属性},其中竖线前面的字母x称为集合的代表元素,在研究集合问题中首先必须弄清集合的代表元素的含义,否则解题时会陷入困境或误入歧途. A note that the attributes of a collection element represent the general form of the collection in descriptive terms: {(?) has a common attribute}, where the letter x in front of the vertical line is called a representative element of the collection. In the study of the collection problem, the collection must first be clarified. Represents the meaning of the element, otherwise it will fall into trouble or go astray when solving the problem.