![](https://video.ask-data.xyz/img.php?b=https://iknow-pic.cdn.bcebos.com/d8f9d72a6059252dc1ad047a249b033b5bb5b911?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto)
(1)
作AD平分∠BAC,交BC于D,则
∠BAD=∠CAD
∵∠B=∠C,AD是公共边
∴△BAD≌△CAD
∴AB=AC
(2)
作BD平分∠ABC,角AC于D,CE平分∠ACB,交AB于E,则
∠ABD=∠CBD=1/2ABC,∠ACE=∠BCE=1/2∠ACB
∵∠ABC=∠ACB
∴∠ABD=∠CBD=∠ACE=∠BCE
∵BC是公共边
∴△BCE≌△CBD
∴BD=CE
∵∠BAD=∠CAE
∴△BAD≌△CAE
∴AB=AC
(3)
作BD⊥AC于D,CE⊥AB于E,则
∠BDC=∠BDA=∠CEB=∠CEA=90°
∵∠ABC=∠ACB
∴∠DBC=∠ECB,∠DBA=∠ECA
∵BC是公共边
∴△DBC≌△ECB
∴BD=CE
∴△ABD≌△ACE
∴AB=AC