帮忙算一下这道题1-1/2+1/6+1/12+1/20+1/30+1/40+1/50+1/70+1/90=?

1+1-1/2+1/2-1/3+...+1/5-1/6+1/40+1/50+1/70+1/90
=11/6+1/40+1/50+1/70+1/9-1/10
=4/3-11/200+1/70
=5429/4200

＝1-1/2＋1/2－1/3＋1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10
＝1-1/10
＝9/10

1-1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90
=(1-1/2)+(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+(1/5-1/6)+(1/6-1/7)+(1/7-1/8)+(1/8-1/9)+(1/9-1/10)
=1-1/10
=9/10