AB=2BC,BC=1/3AC
M为AC的中点,MC=1/2AC
MC-BC=BM=1/6AC,AC=12cm,AB=8cm,BC=4cm
AD=2AB=16cm,
DC=AD+AC=28cm
BD=DC-BC=24cm
N为BD的中点,DN=1/2BD=12cm
AB=2BC,BC=1/3AC
M为AC的中点,MC=1/2AC
MC-BC=BM=1/6AC,AC=12cm,AB=8cm,BC=4cm
AD=2AB=16cm,
DC=AD+AC=28cm
BD=DC-BC=24cm
N为BD的中点,DN=1/2BD=12cm