1 , ,.,ABCABC , AB= AB ,BC =BC, A C =AC.ABCABC,A ,B,C, , 1BC=BC 2B,CAB,ACA 3AB,A C ., SSS,ABC DEF, ABC DEFSSS.,1 AB =AC AD A BC D ABD ACD ,AD,AB=AC,BD=CD,DBC, D BC BD =DC ABD ACD , ABD ACD SSS ,AOB AOB=AOB,2 ,O,D,B,C,A,O,C,A,B,D , 1O OA OB CD 2OAOOC OAC 3CCD 2 D 4D仭OBAOB=AOB,AOB AOB=AOB, ABCDCB. ABCDCB AB = DC AC = DB = ,BC,CB,DCB,ABC .,SSS,1.AB=CDAC=BDABCDCB.,=,=,2.DFBCAB=CEAF=DE ABFECD .,BF=CD, BD=FC,3. AC=FEAD=FB,BC=DE. (1)ABCFDE; (2) C= E.,(1) AD=FB AB=FD. ABCFDE ,AC=FE BC=DE AB=FD ABCFDESSS,=,=,?,?,2 ABCFDE., C=E., SSS),1. . 2. .,