Cho tam giác ABC vuông tại A, đường cao AH. Gọi E, F là hình chiếu của H trên AB, AC. Cho AB = 3cm, BC = 5cm a. Tính AC và Sabc b. Tứ giác AEHF là hình gì? c. Chứng minh tam giác AFH đồng dạng với tam giác HFC. Từ đó suy ra HF^2 = AF. FC d. CM: AH^2 = AE . AB và AE . AB = AF . AC e. CM: Nếu diện tích tam giác AEF bằng 1/4 diện tích tam giác ABC thì tam giác ABC là tam giác vuông cân Mọi người giúp mình bài này với tối nay mình nộp bài rồi:>

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