For sets A, B: A × B = B × A iff:
ASame cardinality
BNever
CA = B (or one of them empty)
DAlways
Answer & Solution
Correct answer: C. A = B (or one of them empty)
A × B and B × A consist of ordered pairs. A × B = B × A iff every (a, b) in A × B also belongs to B × A. Requires A = B (or both empty). Hence Cartesian product is generally NOT commutative.
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