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Let f : A → B be an injective (one-to-one) function.
Define g : 2A → 2B as :
g(C) = {f(x) | x ∈ C}, for all subsets C of A.
Define h : 2B → 2A as :
h(D) = {x | x ∈ A, f(x) ∈ D}, for all subsets D of B.
Q. 
Which of the following statements is always true ?
  • a)
    g(h(D)) ⊆ D
  • b)
    g(h(D)) ⊇ D
  • c)
    g(h(D)) ∩ D = ф
  • d)
    g(h(D)) ∩ (B - D) ≠ ф
Correct answer is option 'A'. Can you explain this answer?
Most Upvoted Answer
Let f : A → B be an injective (one-to-one) function.Define g : 2A...
Understanding the Functions
Let’s break down the functions defined:
- f : A → B is an injective function, meaning each element in A maps to a unique element in B.
- g : 2A → 2B is defined as \( g(C) = \{f(x) | x \in C\} \); it maps subsets of A to subsets of B.
- h : 2B → 2A is defined as \( h(D) = \{x | x \in A, f(x) \in D\} \); it maps subsets of B back to subsets of A.
Exploring the Statements
Now, let’s analyze the statements provided:
1. g(h(D)) ⊆ D
2. g(h(D)) ⊇ D
3. g(h(D)) ∩ D = ∅
4. g(h(D)) ∩ (B - D) ≠ ∅
Why is Option A (g(h(D)) ⊆ D) Always True?
- If \( y \in g(h(D)) \), then there exists \( x \in h(D) \) such that \( y = f(x) \).
- Since \( x \in h(D) \), it follows that \( f(x) \in D \) (by the definition of h).
- Thus, \( y \in D \).
- This shows that every element produced by g from h(D) is indeed in D.
Why Other Options Are Not Always True?
- Option B (g(h(D)) ⊇ D): Not true, as g(h(D)) may not cover all elements of D.
- Option C (g(h(D)) ∩ D = ∅): Not true, as some elements in g(h(D)) can be in D.
- Option D (g(h(D)) ∩ (B - D) ≠ ∅): Not guaranteed, as g(h(D)) could be entirely contained in D.
Conclusion
Therefore, the only universally valid statement is g(h(D)) ⊆ D, confirming that option A is correct.
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Let f : A → B be an injective (one-to-one) function.Define g : 2A → 2B as :g(C) = {f(x) | x ∈ C}, for all subsets C of A.Define h : 2B → 2A as :h(D) = {x | x ∈ A, f(x) ∈ D}, for all subsets D of B.Q.Which of the following statements is always true ?a)g(h(D)) ⊆ Db)g(h(D)) ⊇ Dc)g(h(D)) ∩ D = d)g(h(D)) ∩ (B - D) ≠ Correct answer is option 'A'. Can you explain this answer?
Question Description
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