

InterviewSolution
1. |
For any sets A, B and C prove that: A × (B – C) = (A × B) – (A × C) |
Answer» Given: A, B and C three sets are given. Need to prove: A × (B – C) = (A × B) – (A × C) Let us consider, (x, y)∈A × (B – C) ⇒ x∈A and y∈(B – C ) ⇒ x∈A and (y∈B and y ∉ C) ⇒ (x∈A and y∈B) and (x∈A and y ∉ C) ⇒ (x, y)∈(A × B) and (x, y) ∉ (A × C) ⇒ (x, y)∈(A × B) – (A × C) From this we can conclude that, ⇒ A × (B – C) ⊆ (A × B) – (A × C) ...... (1) Let us consider again, (a, b)∈(A × B) – (A × C) ⇒ (a, b)∈(A × B) and (a, b) ∉ (A × C) ⇒ (a∈A and b ∈B) and (a∈A and b ∉ C) ⇒ a∈A and (b∈B and b ∉ C) ⇒ a∈A and b∈(B – C) ⇒ (a, b)∈A × (B ∪ C) From this, we can conclude that, ⇒ (A × B) – (A × C) ⊆ A × (B – C) ......... (2) Now by the definition of set we can say that, from (1) and (2), A × (B – C) = (A × B) – (A × C) [Proved] |
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