Bài 2: Tích vô hướng của hai vectơ

Trả lời câu hỏi Toán 10 Hình học Bài 2 trang 44 : Trên mặt phẳng tọa độ Oxy cho ba điểm A(2; 4), B(1; 2), C(6; 2). 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