For any two sets A and B, show that the following statements are equivalent:
A ∪ B = B
We need to show that 3 ⇒ 4
Assume that A ∪ B = B
To show: A ∩ B = A.
∵A ∪ B = B
∴ A⊂ B and so A ∩ B = A.
So (3) ⇒ (4) is true.