We have
[tex]\begin{gathered} (A\cup B)^{\prime}=U-(A\cup B)=\mleft\lbrace1,2,3,4,5,6,7\mright\rbrace-\mleft\lbrace2,3,4,5,6\mright\rbrace \\ (A\cup B)^{\prime}=\mleft\lbrace1,7\mright\rbrace \end{gathered}[/tex]
Answer: A.
[tex](A\cup B)^{\prime}=\lbrace1,7\rbrace[/tex]
