Câu 1:Cho đường tròn tâm O, đường kính AB = 2R, C là điểm chính giữa cung AB. Hai tiếp tuyến với đường tròn (O) tại A và C cắt nhau ở D. a) Chứng minh AOCD là hình vuông. b) Tính diện tích phần nằm ngoài hình thang ABCD của hình tròn (O) theo R. c) Trên đoạn DC lấy điểm E sao cho DE = 1 3 DC. Trên đoạn BC lấy điểm F sao cho EF = EA. Kẻ FG vuông góc với đường thẳng DC (G ∈ DC). Tính độ dài đoạn từng CG theo R. Câu 2 Biết rằng các số x, y thỏa mãn điều kiện x+y=1. Tìm giá trị nhỏ nhất của biểu thức C = x^2+y^2+xy

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