12.2 1 , ,1. ,2., ,滭ABC AB=4cmBC=6cmCA=5cm,1. AB=4cm., :,2. AB5cm 6cm C.,3. CACB., 1 2,ABC,SSS,ABAB,ACAC ,BCBC, ABC ABCSSS,ABC ABC, , ABC DCB AB = CD AC = BD = , ABC ,BC,CB,DCB,AB=CDAC=BDABC DCB,SSS,2ABCABACAD ABCADBC,DBC BD=CD ABDACD,ABAC ADAD DBDC, ABD ACDSSS,1= 2( 1+2=180o,1= BDC90o,AD BC壩,AD BC,BD=CE BD-ED=CE-ED, BE=CD,1:AB=ACAE=ADBD=CE AEB ADC,3ABCDADCB BD,AC, BD,AC,:.,2BECFABDEACDFBECFAD,BECF, BCEF,ABCDEF,ABDE,ACBF,BCEF,ABCDEFSSS,AD(, BE+EC=CF+EC,3 AOBOAOBOM=ONMNCOCAOB,MN CM=CN.,: .AB = DC , AC = DB : 1A = D 2 AO=DO,1SSS,2 ;,3,AC=FEBC=DEADBF AD=FB,ABC FDE,2 AB=CDBC=ADA=C AC ,A,C,B,O,D,