... BC = 18dm; AM = 10cm; AN = 8cm MN = ? A 10 M GT KL N B C Gii Xột ABC v ANM ta cú : AM 10 = = AC 15 AN 18 = = AB 12 Mt khỏc, cú chung A AM AN = AC AB Vy ABC P ANM (c.g.c) AB BC 12 18 8. 18 = T ... = 28, 5cm ã ã DBA = DBC x KL D C x =? Gii ã ã ABD v BDC cú : DAB = DBC (gt) à B1 = D1 ( so le AB // CD) ABD P BDC (g.g) x AB BD 12,5 = hay = 28, 5 BD DC x x = 12,5 28, 5 x = 12,5 28, 5 18, 9(cm) ... d x= = a(1+ ) b+c b+c 1, Thay s ta c AH = 1,6 (1 + ) = 3 ,84 (m) 0, + 0, Vy cao AH bng 3 ,84 A Bi ngh: B C Mt ging nc cú ng kớnh DE = 0,8m (nh hỡnh v) xỏc nh sõu BD ca ging, ngi ta t mt chic...