If A and B are two sets such that A⊂B, then what is A∪B?
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Solution
Let x∈A∪B ⇒x∈Aorx∈B Since, A⊂B ⇒x∈B But x is an arbitrary element of set A∪B. A∪B⊂B ....(1) Let y∈B ⇒y∈A∪B But y is an arbitrary element of set B B⊂A∪B ....(2) From (1) and (2), we get A∪B=B