Answer
Done below.
Work Step by Step
a) $A \cup U = \{x : x \in A \vee x \in U \} = \{x : x \in A \vee T \} = \{x : T \} = U$
b) $A \cap \emptyset = \{x : x \in A \wedge x \in \emptyset \} = \{x : x \in A \wedge F \} = \{x : F\} = \emptyset$
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