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DO是△DEF的角平分線.證明:∵AD是△ABC的角平分線,∴∠CAD=∠BAD.∵DE‖AB,DF‖AC,∴∠EDA=∠FAD,∠FDA=∠EAD,∴∠EDA=∠FDA.∴DO是△DEF的角平分線.
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