作业帮1/12+1/20+1/30+1/42+1/56+1/72+1/90
来源：学生作业帮助网 编辑：作业帮 时间：2024/04/28 01:17:25
1/12+1/20+1/30+1/42+1/56+1/72+1/90
1/12+1/20+1/30+1/42+1/56+1/72+1/90
1/12+1/20+1/30+1/42+1/56+1/72+1/90
=1/3*4+1/4*5+1/5*6+1/6*7+1/7*8+1/8*9+1/9*10
=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
=1/3-1/10
=7/30
【通项：
1/n(n+1)=1/n-1/n+1】
1/12=1/3-(1/4)
1/20=1/4-(1/5)
……
1/90=1/9-(1/10)
1/12+1/20+1/30+1/42+1/56+1/72+1/90
=1/3-(1/4)+(1/4)-(1/5)+……+(1/9)-(1/10)
=1/3-(1/10)
=7/30
1/12+1/20+1/30+1/42+1/56+1/72+1/90
=(1/3-1/4)+(1/4-1/5)+……+(1/9-1/10)
=1/3-1/10
=7/30
因为1/12 =1/(3×4）=1/3-1/4
所以
1/12+1/20+1/30+1/42+1/56+1/72+1/90
=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
=1/3-1/10
=7/30
1/6+1/12+1/20+1/30+1/42
1/3-1/12-1/20-1/30-1/42
1／6+1／12+1／20+1／30+1／42
1/12+1/20+1/30+1/42+.+1/2450
1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72
1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72
1/2+1/6+1/12+1/20+1/30+1/42+1/56 简算
1/2+1/6+1/12+1/20+1/30+1/42+1/56简算,
1/12+1/20+1/30+1/42+1/56+1/72+1/90
简便运算：1/2+1/6+1/12+1/20+1/30+1/42+1/56
1+1/2+1/6+1/12+1/20+1/30+1/42的简便计算
2/1+6/1+12/1+20/1+30/1+42/1+56/1=?
1/12+1/20+1/30+1/42+1/56+1/72+1/90
1/6+1/12+1/20+1/30+1/42+1/56+1/72 简便计算
1/2 - 1/6 - 1/12 - 1/20 - 1/30 - 1/42 - 1/56怎么算
1+1/2+1/6+1/12+1/20+1/30+1/42=?
1/2+1/6+1/12+1/20+1/30+1/42+1/56
1/2-1/6-1/12-1/20-1/30-1/42-1/56等于多少