【纠正:EF//AB】
证明:
∵EF//AB
∴⊿DEM∽⊿DAB,=>EM/AB=DE/DA
⊿CFN∽⊿CBA,=>FN/AB=CF/CB
∵AB//EF//DC
∴AE/DE=BF/CF=>AE/DE+1=BF/CF+1
=>(AE+DE)/DE=(BF+CF)/CF
=>DA/DE=CB/CF=>DE/DA=CF/CB
∴EM/AB =FN/AB
∴EM=FN
【纠正:EF//AB】
证明:
∵EF//AB
∴⊿DEM∽⊿DAB,=>EM/AB=DE/DA
⊿CFN∽⊿CBA,=>FN/AB=CF/CB
∵AB//EF//DC
∴AE/DE=BF/CF=>AE/DE+1=BF/CF+1
=>(AE+DE)/DE=(BF+CF)/CF
=>DA/DE=CB/CF=>DE/DA=CF/CB
∴EM/AB =FN/AB
∴EM=FN