Cho tam giác ABC vuông tại A. Cho biết AB = 6cm, AC = 8cm. a) Tính cạnh BC và góc B (góc làm tròn đến độ). b) Gọi H là hình chiếu của A trên BC. Tính AH. c) Kẻ HE vuông góc AB (E thuộc AB). Chứng minh: AE.AB = HB.HC d) Kẻ HF vuông góc AC ( F thuộc AC ). Gọi K là trung điểm của BC. Chứng mình : AK vuông góc EF

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