Finding AF / ad = ad / AB in triangle ABC by de / / BC EF / / CD

Finding AF / ad = ad / AB in triangle ABC by de / / BC EF / / CD

∵DE//BC ∴△ADE∽△ABC ∴AD/AB=AE/EC
∵EF//CD ∴△AFE∽△ADC ∴AF/AD=AE/EC
∴AF/AD=AD/AB