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3。过D点作AB的垂线：DE 得∠DEA=90°∵AD平分∠CAB ∠C=90°∴∠CAD=∠DAB∴△CAD≌△DAE∴CA=AE=6 CD=DE∴BE=6√2-6∵AC=BC ∴∠B=45° ∴△DEB是等腰直角三角形∴DE=BE=CD=6√2-64。①(4,0) (-4,0)②AB=3+5=8∵S△ABC=16=AB*|Cy|/2∴|Cy|=4∴只要点C的纵坐标是 4 或 -4 都能满足5。①∵∠CAE=∠B ∠ACE+∠1+∠2=90°∴∠B+∠1+∠2=90°∴∠AEB=90°∵AD平分∠BAE ∴∠1=∠2过D点做AB垂线：DF得：∠DFA=∠AEB=90°∴△AED≌△ADF∴ED=DF ∵E是CD的中点∴CE=ED=DF∴在△ACE和△DFB中∠ACE=∠DFB CE=DF ∠CAE=∠B∴△ACE≌△DFB∴AC=BD②成立在AB上找一点H 使∠AHD=∠AED∵∠1=∠2 AD是公共边∴△AED≌△AHD ∴DE=DH∵∠AEC=180°-∠AED∠DHB=180°-∠AHD∴∠AEC=∠DHB∵CE=DE∴CE=DH△ACE≌△DHB （AAS）∴BD=AC