设MN与EF交于点P．∵NE∥BC，∴△PNE∽△PBC，∴PNPB＝PEPC，∴PB•PE=PN•PC．又∵ME∥BF，∴△PME∽△PBF，∴PMPB＝PEPF，∴PB•PE=PM•PF．∴PN•PC=PM•PF，故PMPN＝PCPF，又∠FPN=∠MPE，∴△PNF∽△PMC，∴∠P...