延长AD至E,使AD=DE，连结CE∵AD是中线∴BD=CD∵∠ADB=∠CDE∴⊿ABD≌⊿CDE∴AB=CE=5∵AE=AD+DE=6+6=12AC=13∴AC²=AE²+CE²∴∠AEC=90°∴S⊿ACE=½×CE×AE=½×5×12=30∴S∠ABC=S⊿ACE=30
