1/2,-1/6,1/12,-1/20,1/30

1/2,-1/6,1/12,-1/20,1/30 1/2+1/6+1/12+1/20+1/30 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+.+1/9900=? 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 简算 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= 1/2-1/6-1/12-1/20-1/30-1/42-1/56等于多少 1/2+1/6+1/12+1/20+1/30+1/42+1/56简算, 2/1+6/1+12/1+20/1+30/1+42/1+56/1=?