A123Bxyx的精選

問題詳情：已知*A={1,2,3},B={(x,y)|x∈A,y∈A,x+y∈A},則*B的子集的個數為()(A)4   (B)7   (C)8   (D)16 【回答】C解析:因為*A={1,2,3},B={(x,y)|x∈A,y∈A,x+y∈A},所以*B={(1,1),(1,2),(2,1)},*B的子集的...