Question

AB//GH//CD,点H在Bc上,Ac与BD交于点G,求证1/AB+1/CD=1/GH

第二个图 急！

Answer 1

解：∵AB∥GH CD∥GH
∴GH/AB=CH/BC GH/CD=BH/BC
相加，GH/AB+GH/CD=(CH+BH)/BC=BC/BC=1
∴GH(1/AB+1/CD=1
即GH（1/2+1/3）=1
∴GH=6/5

Answer 2

∵AB∥CD∥GH，∴GH/AB=CG/AC,GH/CD=AG/AC,两式左右相加得
GH/AB+GH/CD=CG/AC+AG/AC=1
∴ 1/AB+1/CD=1/GH