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Question
For any two sets of A and B, prove that:
\[A' \cup B = U \Rightarrow A \subset B\]
Solution
\[\ \text{ Let } a \in A . \]
\[ \Rightarrow a \in U\]
\[ \Rightarrow a \in A' \cup B \left( \because U = A' \cup B \right)\]
\[ \Rightarrow a \in B \left( \because a \not\in A' \right)\]
\[\text{ Hence }, A \subset B . \]
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