∵∠ACD=∠ECB,即∠ACB+∠BCD=∠ECD+∠BCD,则∠ACB=∠ECD在△ACB和△ECD中,AC=CE,CB=CD,∠ACB=∠ECD,∴△ACB≌△ECD,得AB=DE
∠ACD=∠ECB,∠ACD-∠BCD=∠ECB-∠BCD,∠ACB=∠ECD,BC=CD,AC=CE,边角边全等∴△ACB≌△ECD,得AB=DE
有∠ACD=∠ECB,∠BCD为其公共角,即∠ACB=∠ECD,如此一来利用“边角边定理”证得△ACB≌△ECD,即可证得AB=ED