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问题: (3)大家来看看关于数学的^&^

诺集合{0,1,2}∪(a,2)={-1,0,1,2},则a=_____

解答:

集合{0,1,2} ∪ {a,2} = {-1,0,1,2},
由于集合{0,1,2}中没有“-1”,而集合{-1,0,1,2}中有“-1”
所以集合{a,2}中必须有“-1”
故 a = -1
(检验知正确)