Question

如图，已知AD∥BC，∠A=∠C，试说明：AB∥CD．

Answer

答案见解析．

【解析】由于AD∥BC，易得∠A=∠ABF，而∠A=∠C，等量代换可得∠ABF=∠C，从而可证AB∥CD．

如图所示．

∵AD∥BC，∴∠A=∠ABF．

∵∠A=∠C，∴∠ABF=∠C，∴AB∥CD．