Question

1/18+1/54+1/108+1/180+1/270+1/378+1/504+1/648+1/810+1/990怎么求

Answer 1

最终结果=1/18{1/[n*(2n-1)]+1/[n*(2n+1)]} ;(n=1,2,3,4,5);

Answer 2

原式=1/3*6+1/6*9+1/9*12+……+1/30*33=1/3[(1/3-1/6)+(1/6-1/9)+(1/9-1/12)……(1/30-1/33)]=1/3(1/3-1/33)=10/99