Câu 1 . Cho tập hợp X, gồm các bạn học sinh có tên sau: An, Nam, Bình, Hoa, Thắng. Tập Y gồm các số: 1,2,3,4,5. Anh chị hãy thiết lập ánh xạ f từ X vào Y thỏa mãn một trong các tính chất sau: a) f là ánh xạ không đơn ánh. b) f là song ánh.

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