1.d在ab上,因为点c是线段ab中点,则bc=ab/2,bd = 3ab/5,ad=2ab/5又因为cd+bc=bd,则cd=bd-bc=3ab/5-ab/2=ab/10,因为cd=2cm,所以ab=20cm,ad=2*20/5=8cm2.d在ab的延长线上,因为点c是线段ab中点,则cb=ab/2,bd = 3ab/5,ad=...