If A ⊆ B in a universal set U, which of the following relations is always true?
Answer and explanation
Correct answer: B′ ⊆ A′
A ⊆ B means that every element of A is also an element of B. Consider any element x in B′. Since x is not in B, it cannot be in A either; otherwise A ⊆ B would force x to be in B. Therefore x belongs to A′, proving B′ ⊆ A′. Taking complements reverses the direction of inclusion, so option A is correct.
Frequently asked questions
What is the correct answer to this question?
B′ ⊆ A′
Why is this the correct answer?
A ⊆ B means that every element of A is also an element of B. Consider any element x in B′. Since x is not in B, it cannot be in A either; otherwise A ⊆ B would force x to be in B. Therefore x belongs to A′, proving B′ ⊆ A′. Taking complements reverses the direction of inclusion, so option A is correct.
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.