Question

帮帮忙，用简便计算

Answer 1

 

Answer 2

 

追问

还有个呢

追答

1/2+1/6+1/12+1/20+1/30+....+1/72+1/90 = 1/1*2 +1/2*3 +1/3*4 +...+1/8*9 +1/9* 10 = (1/1 -1/2)+(1/2 -1/3)+...+(1/8 -1/9)+(1 /9 -1/10) = 1/1 -1/10 = 9/10

1/2+1/6+1/12+1/20+1/30+....+1/72+1/90 = 1/1*2 +1/2*3 +1/3*4 +...+1/8*9 +1/9* 10 = (1/1 -1/2)+(1/2 -1/3)+...+(1/8 -1/9)+(1 /9 -1/10) = 1/1 -1/10 = 9/10

1/2+1/6+1/12+1/20+1/30+....+1/72+1/90 =
1/1*2 +1/2*3 +1/3*4 +...+1/8*9 +1/9* 10 =
(1/1 -1/2)+(1/2 -1/3)+...+(1/8 -1/9)+(1 /9 -1/10) =
1/1 -1/10 =
9/10

追问

没有1/2和1/90

Answer 3

采纳

Answer 4

才

Answer 5

我来

追问

特别是下一题

追答

先采纳，我正在算

追问

你放心，只要第二题做出来我肯定采纳

好了没

追答

没