=1997*1999*1996/1998-1995*1997*1999/1998
=(1997*1999*1996)-(1995*1997*1999)/1998
=1997*1999/1998
=[(1997+1)(1999-1)-1]/1998
=(1998*1998-1)/1998
=1998-1/1998
=1997又1997/1998
应该是这样吧