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nguyenhoaibang2k9
2 năm trước
giúp mình hai bài này với ;;v;; . Cho hình bình hành ABCD (A <b Bb). Gọi E là hình chiếu của C trên AB, K là hình chiếu của C trên AD, H là hình chiếu B trên AC. Chứng minh rằng: a) AB.AE = AC.AH b) BC.AK = AC.HC c) AB.AE + AD.AK = AC2 . Cho ∆ABC vuông tại A, đường cao AH, BC = 20cm, AH = 8cm. Gọi D là hình chiếu của H trên AC, E là hình chiếu của H trên AB. a) Chứng minh ∆ADE v ∆ABC. b) Tính diện tích ∆ADE
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