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Answers for “为什么在关系的定义中使用有序对?”

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Understand why

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Ordered pairs are used because the order of the elements matters in a relation. The first component of the pair is related to the second component, and swapping them can change whether the relationship holds.

Conditions: The relation is between two sets A and B.; The relationship is directional or asymmetric.

Find a method

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The video tests the less-than relation with two reversed ordered pairs: (2, 5) and (5, 2). It shows that 2<52 < 5 is true, so the pair (2, 5) belongs to the relation.

Conditions: The relation is the less-than symbol (<) on integers.; The pairs tested are (2, 5) and (5, 2).

Meet the concept

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In the definition of a relation, capital letters A and B denote the sets themselves, while lowercase letters a and b denote individual elements belonging to those sets. The ordered pair (a, b) represents a specific element of the Cartesian product A×BA \times B, where a is an element of A and b is an element of B.

Conditions: The context is the formal definition of a relation R between sets A and B.; The notation (a, b) ∈ A×BA \times B is used.

Meet the concept

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A relation R between two sets A and B is formally defined as a subset of the Cartesian product A×BA \times B. This means that R is a collection of ordered pairs, where the first element of each pair belongs to set A and the second element belongs to set B.

Conditions: A and B are sets.; R is a binary relation between A and B.