4/7-2/9+3/7-2/9=(4/7+3/7)-(2/9+2/9)=1-4/9=5/9望采纳
4/7-2/9+3/7-2/9=(4/7+3/7)-(2/9+2/9)=1-4/9=5/9
4/7-2/9+3/7-2/9=4/7+3/7-2/9-2/9=(4/7+3/7)-(2/9+2/9)=1-4/9=5/9