举报
looeywang
1/1乘于3+1/3乘于5+1/5乘于7+1/7乘于9+... ...+1/2007乘于2009. =½（1-1/3+1/3-1/5+……+1/2007-1/2009) =½(1-1/2009) =½×2008/2009 =1004/2009 题目自己改下 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 =3/10
