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Answers for “笛卡尔积对并集和交集满足哪些分配律?”

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Meet the concept

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The Cartesian product distributes over both union and intersection from both the left and the right. Specifically, (A ∪ B) × C=(A×C)C = (A \times C) ∪ (B×CB \times C), (A ∩ B) × C=(A×C)C = (A \times C) ∩ (B×CB \times C), A × (B ∪ C) = (A×BA \times B) ∪ (A×CA \times C), and A × (B ∩ C) = (A×BA \times B) ∩ (A×CA \times C).

Conditions: A, B, and C are arbitrary sets.

Find a method

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The distributive law (A ∪ B) × C=(A×C)C = (A \times C) ∪ (B×CB \times C) can be understood by treating sets as lengths of line segments and Cartesian products as areas of rectangles. The area of a large rectangle with width A ∪ B and height C equals the sum of the areas of two smaller rectangles with widths A and B, and height C.

Conditions: A, B, and C are arbitrary sets.; The geometric analogy treats sets as lengths and Cartesian products as rectangular areas.

Find a method

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To compute the Cartesian product of two finite sets, systematically pair each element of the first set with every element of the second set, and list all resulting ordered pairs in a new set.

Conditions: The sets are finite and explicitly given.

Understand why

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No, (A×BA \times B) ∪ (C×DC \times D) generally does not equal (A ∪ C) × (B ∪ D). While the intersection of two Cartesian products is a Cartesian product, their union is typically an irregular shape (like an L-shape) that cannot be expressed as a single Cartesian product of two sets.

Conditions: A, B, C, and D are arbitrary sets.

Meet the concept

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The intersection of two Cartesian products (A×BA \times B) and (C×DC \times D) is equal to the Cartesian product of the intersections of their respective component sets, i.e., (A ∩ C) × (B ∩ D).

Conditions: A, B, C, and D are arbitrary sets.

Meet the concept

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The Cartesian product of two sets A and B, denoted A×BA \times B, is the set of all possible ordered pairs (x, y) where the first element x belongs to set A and the second element y belongs to set B.

Conditions: A and B are arbitrary sets.