2001=2002-1,2003=2002+1 2001/(2001+2002/2003)+1/2003=（2002-1）/[(2002-1)+2002/(2002+1)]+1/(2002+1)=(2002-1)/{[(2002-1)(2002+1)+2002]/(2002+1)}+1/(2002+1)=(2002-1)（2002+1）/[(2002-1)(2002+1)+2002]+1/...