dandiao123
春芽
共回答了18个问题采纳率:88.9% 举报
裂项法:
3/2一17/6十37/12一99/20+151/30-291/42+393/56-647/72+811/90
=1+1/2一3+1/6十3+1/12一5+1/20+5+1/30-7+1/42+7+1/56-9+1/72+9+1/90
=(1-3+3-5+5-7+7-9+9)+(1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90)
=1+(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+(1-1/10)
=1+9/10
=1.9
1年前
7