∴ 180 -∠3=∠DBA， 180 -∠4=∠CBA

∴∠DBA=∠CBA

In △ ADB and △ACB,

∠ 1=∠2 (known)

AB=AB (male side)

∠DBA=∠CBA (certification)

∴△ADB≌△ACB(ASA)

∴AC=AD (the corresponding sides of congruent triangles are equal)

Prove that the distance from ∵C to A and D is equal.

∴AC=BC

In delta △ACD and delta △CEB

AC=BC (certification)

∠CEB=∠CDA (known)

∠C=∠C (angle * * *)

∴△ACD≌△CEB

∴AD=BE (the corresponding sides of congruent triangles are equal)

(1) Prove that the advertisement of (6) is high.

∴∠ADC=∠ADB=90

In RT△ADC and RT△ADB.

AD=AD (male side)

AB=AC (known)

∴△ADC≌ADB(HL)

∴BD=CD (the corresponding sides of congruent triangles are equal)

(2) Proof: ∫△ADC≌ADB (proven)

∴∠BAD=∠CAD

⒏ It is proved that ∵AC⊥CB,AB⊥DC.

∴∠C=∠B=90

In ACB and DBC.

AB=DC (known)

CB=CB (male * * * side)

∴RT△ACB≌RT△DBC(HL)

∴∠ABD=∠ACD (the angles corresponding to congruent triangles are equal).

⒑ in Delta△ △AOB and Delta△ △DOC

OA=OC (known)

OB=OD (known)

∠AOB=∠DOC (equal to the vertex angle)

∴△AOB≌△DOC(SAS)

∴∠DCO=∠BAO (the corresponding angles of congruent triangles are equal).

∴DC∥AB (parallel method)

⒒∵ B, F, C, E are in a straight line, ab∨de, AC∨df.

∴∠ABC=∠DEF,∠ACB=∠DFE

∠ACB=∠DFE

∴FB﹢FC=BC,CE﹢FC=EF

∴BC=EF

In delta △DFE and delta △ACB

∠ABC=∠DEF (authentication)

∠ACB=∠DFE (certification)

BC=EF (certification)

∴△DFE≌△ACB(ASA)

∴AB=DE,AC=DF (the corresponding sides of congruent triangles are equal).