... 32/ 77 (SGK) a) Xẹt ∆OCB v ∆OAD, c : 5 8 OD OB OA OC == v O chung => ∆OCB ∆OAD (c. g .c) b) Vç ∆OCB ∆OAD (c u a) => B = D Xẹt ∆IAB v ∆ICD, c : I 1 = I 2 ( äúi âènh) B = D (c/ m trãn) => ... = 50 0 [?2] a) C 3 tam gi c, âọ l: ∆ABC, ∆ADB, ∆BDC Xẹt ∆ABC v ∆ADB c : A chung C = ABD (gt) => ∆ABC ∆ADB (g-g) b) Vç ∆ABC ∆ADB (c u a) => AB AC AD AB = hay 3 5, 4 x 3 = => x = 2 (cm) ... => y = AC - AD = 4 ,5 - 2 = 2 ,5 (cm) c) C BD l phán gi c g c B (gt) => BC BA DC DA = hay BC 3 5, 2 2 = Ngỉåìi Soản --- Tráưn Hỉỵu Trung 1 45 A 4, 5 B C 3 x D y Trổồỡng THCS Ma c ộnh Chi Hs:...