2/7×9+3/9×15+4/15×23+5/23×33

2/7×9+3/9×15+4/15×23+5/23×33
=1/7-1/9+0.5(1/9-1/15)+0.5*(1/15-1/23)+0.5(1/23-1/33)
=1/7-1/18-1/66
=50/693

2/7×9+3/9×15+4/15×23+5/23×33
=(1/7-1/9)+(1/9-1/15)/2+(1/15-1/23)/2+(1/23-1/33)/2
=(1/7-1/9)+(1/9-1/15+1/15-1/23+1/23-1/33)/2
=1/7-1/9+(1/9-1/33)/2
=1/7-1/9+1/18-1/66
=50/693

你题目是否有错？
是不是1/7×9+3/9×15+4/15×23+5/23×33？
如果是则

1/7×9+3/9×15+4/15×23+5/23×33
=(1/7-1/9)/2+(1/9-1/15)/2+(1/15-1/23)/2+(1/23-1/33)/2
=(1/7-1/9+1/9-1/15+1/15-1/23+1/23-1/33)/2
=(1/7-1/33)/2
=13/231

1/7-1/9+1/2(1/9-1/15)+1/2(1/15-1/23)+1/2(1/23-1/33=

好久没接触了，帮不了你了