The word "set" in mathematics is similar to "all", "one kind", "one group", "all" and "whole" in our daily life. The elements in a set are out of order, which is the disorder of elements. As long as the elements that make up two sets are the same, we say that the two sets are equal.
For example, which of the following objects is the set _ _ _ _ _.
Until now, the students are still surfing the Internet in the classroom.
② All people in the world who are over 1.6 meters tall.
All the tall people in the world
At this moment, the five tallest people in the world are a whole.
Analysis: judging whether a description is a set depends on whether it conforms to the characteristics of the set: certainty and difference.
The description in (1) is this moment, which is a definite time; The students who surf the Internet in the classroom are different individuals. Therefore, the description of items conforms to the characteristics of sets: certainty and difference. So the description is a collection.
The height above 1.6m described in is a certain height, and these people are also different. So it is also a collection.
"All the tallest people in the world" and "tallest people" are uncertain, and there is no definition of how tall they are. Uncertainty, so it is not a set.
The five tallest people described in the book, which is certain, are the five tallest people. We shouldn't know who these five people are, but they do exist. So this item is also a set.
To sum up, what meets the setting is 124.
Extended data:
Characteristics of sets
1, certainty
Given a set, any element, whether it belongs to the set or not, must be one of them, and no ambiguity is allowed.
2. Interrelation
Any two elements in a collection are considered different, that is, each element can only appear once. Sometimes it is necessary to describe the situation where the same element appears many times. You can use multiset, where elements are allowed to appear multiple times.
3. Chaos
In a set, the state of each element is the same and the elements are out of order. You can define an order relation on the set. After defining the order relation, you can sort the elements according to the order relation. But as far as the characteristics of the set itself are concerned, there is no necessary order between elements? .
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