(1)证△BCH∽△ECD, △CGH∽△CFD, BC/CE=CH/CD=GH/DF, ∴GH·CE=DF·BC(2)证△DFC∽△DCE (3)证△CGH∽△ECD(4)证△BCG∽△ACB, △BCH∽△CGH, GB/BA=GC/BC=CH/BH, ∴GB∶BA=CH∶BH.(5)证△ACB∽△ECF, △DFC∽△HCB, BA/EF=BC/CF=CH/DF, ∴CH·EF=BA·DF.