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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