Let A and B be two non-empty subsets of set X such that A is not a sub...
Explanation:
To understand why option D is always true, let's analyze the given information step by step.
1. A is not a subset of B:
This means that there exists at least one element in A that is not in B. Let's call this element "x".
2. A is a subset of the complement of B:
To prove this, we need to show that every element in A is also in the complement of B.
- Let's assume that there exists an element "y" in A that is not in the complement of B. This would mean that y is in B.
- Since A is not a subset of B (as stated in the question), there must be an element "x" in A that is not in B.
- But we already know that x is not in B, so y cannot be equal to x.
- Therefore, we have found an element "y" in A that is not in the complement of B, which contradicts our assumption.
- Hence, every element in A must be in the complement of B, making A a subset of the complement of B.
3. A and the complement of B are non-disjoint:
To prove this, we need to show that there exists at least one element that is common to both A and the complement of B.
- Since A is not a subset of B, there exists an element "x" in A that is not in B.
- This means that x must be in the complement of B.
- Therefore, x is a common element to both A and the complement of B.
- Hence, A and the complement of B are non-disjoint.
Conclusion:
Based on the above analysis, we can conclude that option D is always true. A is a subset of the complement of B, and A and the complement of B are non-disjoint.