Answer: the inclusion–exclusion principle.
- A the associative law of sets
- B the inclusion–exclusion principle
- C the distributive law of sets
- D De Morgan’s second law
Correct answer: B. the inclusion–exclusion principle
Explanation: This is the inclusion–exclusion principle: adding the two sizes double-counts the overlap, so it is subtracted once.
A Venn diagram makes set identities visual: A∪B is everything inside either circle, A∩B is only the overlap, and the region outside both circles represents the complement of their union - directly illustrating De Morgan's law (A∪B)′ = A′∩B′.
Concept context
Types of sets, operations (union/intersection/complement), relations, and types of functions with domain and range