13.设U={n|n是小于9的正整数}.A={n∈U|n是奇数}.B={n∈U|n是3的倍数}.则∁U= [解析] ∵U={1,2,3,4,5,6,7,8}.A={1,3,5,7}.B={3,6}.∴A∪B={1,3,5,6,7}.∴∁U={2,4,8}. [答案] {2,4,8} 查看更多

 

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