1.

If A × B ⊆ C × D and A × B ≠ ϕ, prove that A ⊆ C and B ⊆ D.

Answer»

Given: A × B ⊆ C × D and A × B ≠ ϕ 

Need to prove: A ⊆ C and B ⊆ D 

Let us consider, (x, y) (A × B)......... (1) 

⇒ (x, y)∈(C × D) [as A × B ⊆ C × D] .......... (2)

From (1) we can say that,

x∈ A and y∈B .......... (a) 

From (2) we can say that, 

x∈C and y∈D ....... (b) 

Comparing (a) and (b) we can say that, 

⇒ x∈A and x∈C 

⇒ A ⊆ C Again, 

⇒ y∈B and y∈D 

⇒ B ⊆ D [Proved]



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