如BC在A的同一侧:AD = AB/2 = 8,AE = AC/2 = 20,DE = AE - AD = 20 - 8 = 12 cm
如BC在A的两侧:AD = AB/2 = 8,AE = AC/2 = 20,DE = AE + AD = 20 + 8 = 28 cm
如BC在A的同一侧:AD = AB/2 = 8,AE = AC/2 = 20,DE = AE - AD = 20 - 8 = 12 cm
如BC在A的两侧:AD = AB/2 = 8,AE = AC/2 = 20,DE = AE + AD = 20 + 8 = 28 cm