问题
选择题
设全集U={1,3,5,7},M={1,a-5},CUM={5,7},则实数a的值为( )
A.-2
B.2
C.-8
D.8
答案
根据题意,有M∪CUM={5,7,1,a-5},
又由补集的性质可得M∪CUM=U,即{5,7,1,a-5}={1,3,5,7},
必有a-5=3,解可得a=8;
故选D.
设全集U={1,3,5,7},M={1,a-5},CUM={5,7},则实数a的值为( )
A.-2
B.2
C.-8
D.8
根据题意,有M∪CUM={5,7,1,a-5},
又由补集的性质可得M∪CUM=U,即{5,7,1,a-5}={1,3,5,7},
必有a-5=3,解可得a=8;
故选D.