Question

已知AB‖EF‖CD,AC,BD交于E点,(1)试说明1/AB +1/CD =1/EF (2)若AB=6厘米,CD=12

Answer 1

1.EF/AB=CF/CB EF/CD=BF/BC EF/AB+EF/CD=CF/CB+BF/BC=BC/BC=1

有1/AB +1/CD =1/EF

2.代人上式 1/6+1/12=1/EF=1/4 EF=4