  F 1  ʼ  G   
  F 2      
  F 3      
һȺӶȺ:302408030
F1+F2 Ʒ12Ʒɽ׵ģȻƷ1F1ȻƷһʼ䣨ʼĵطȻɷ䣬ٰһȥҪһһŶ~Ȼرʼ䣬ʱƷ12䣬ͼF2