If A' ∩ B' = ∅, what is the correct conclusion about A ∪ B?
Answer and explanation
Correct answer: A ∪ B = U
By De Morgan's law, A' ∩ B' = (A ∪ B)'. The condition says that the complement of A ∪ B is empty. A set has an empty complement in U only when it contains every element of U. Therefore, A ∪ B = U, so option B is correct. Equivalently, every element of the universal set belongs to A or to B.
Frequently asked questions
What is the correct answer to this question?
A ∪ B = U
Why is this the correct answer?
By De Morgan's law, A' ∩ B' = (A ∪ B)'. The condition says that the complement of A ∪ B is empty. A set has an empty complement in U only when it contains every element of U. Therefore, A ∪ B = U, so option B is correct. Equivalently, every element of the universal set belongs to A or to B.
Which subject and chapter does this question cover?
This is a Class 10 Mathematics question. Chapter: Sets. Topic: Complement of a Set and Its Properties.