2.4cm
设BC = X ,则AB =3X ,AC = 4X,AD= 3AC = 12X,AE = 3AB = 9X,CE = AE - AC = 9X - 4X = 5X = 4
所以X = 4/5 = 0.8 ,DE = AD -AE = 12X - 9X = 3X = 2.4cm
2.4cm
设BC = X ,则AB =3X ,AC = 4X,AD= 3AC = 12X,AE = 3AB = 9X,CE = AE - AC = 9X - 4X = 5X = 4
所以X = 4/5 = 0.8 ,DE = AD -AE = 12X - 9X = 3X = 2.4cm