1, according to U = {1, 2,3,4,5}, A∪B=U, which should be A∪B = empty set; It can be concluded that sets A and B divide set U equally, and there are no repeated elements;

2. According to the condition that a ∩ (cub) = {1, 2}, we can judge the set a = {1, 2}; The meaning of this condition, the complement of a and b in set u; According to A∪B=U, we can get the set b = {3 3,4,5};

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