梯形ABCD中,AD∥BC,BA、CD相交于点G,AC、BD相交于点F,作直线GH交AD于E,交BC于F∵AD∥BC∴AE/BF＝GA/GB＝AD/BC＝AH/HC＝EH/HF＝ED/BF∴AE＝ED又AE/BF＝GE/GF＝ED/FC∴BF＝FC可见E、F分别是AD、BC的中点,从而说明E、F...