应该是：ef垂直于ab分别交ab、ad于点f、g证明：∵ ac和bd,cd都是圆O的切线∴ CA=CE,BD=ED又 AC⊥AB,BD⊥AB,EF⊥AB∴ AC//EF//DB∴ AF/AB=CE/CD∵ FG/BD=AF/AB∴FG=BD*AF/AB=BD*CE/CDEG/AC=DE/CD∴EG=AC*DE/CD=CE*BD/...