23×（1/5+1/7） 好多人答案都算成23 怎么算的？求解？
23×（1/5+1/7） 好多人答案都算成23 怎么算的？求解？
23×（1/5+1/7）
=23×12/35
=276/35
而不是等于23~
1/2*5+1/3*5+1/8*11+.+1/20*23=？跪求答案
1/2*5+1/5*8+1/8*11+......+1/20*23
=1/3*(1/2-1/5+1/5-1/8+1/8-1/11+1/11-1/13+...+1/17-1/20+1/20-1/23)
=1/3*(1/2-1/23)
=1/3*21/46
=7/46
欢迎采纳，
不胜感激！
\(^o^)/~
1/5+1/4=？求答案
9/20..........
简便计算1/2*5+1/3*5+1/8*11+……＋1∕20*23
题目打错了吧？应该是1/2*5+1/5*8+1/8*11+…+1/20*23=1/3*(1/2-1/5+1/5-1/8+1/8-1/11+…+1/20-1/23)=1/3*(1/2-1/23)=7/46
25*（1/1*3+1/3*5+1/5*7……+1/23*25）
黄拽帅，你好：
25×（1/1*3+1/3*5+1/5*7……+1/23*25）
＝25×〔1/2×（1－1/3＋1/3－1/5＋1/5－1/7＋......＋1/23－1/25）〕
＝25×〔1/2×（1－1/25）〕
＝25×1/2×24/25
＝12
1/3*5+1/5*7+1/7*9……+1/997*999 求解
用裂项法：
1/3*5+1/5*7+1/7*9……+1/997*999
= (1/2)(1/3-1/5)+(1/2)(1/5-1/7)+(1/2)(1/7-1/9)+……+(1/2)(1/997-1/999)
= (1/2)[(1/3-1/5)+(1/5-1/7)+(1/7-1/9)+……+(1/997-1/999)]
= (1/2)(1/3-1/999)
= 166/999
1/71/5+1/51/7怎么简算
=5/7+7/5
=(5x5+7x7)/35
=74/35
a+1/a=5,a的平方+1/a的平方=？、答案是23，请问怎么算
a2 + (1/a)2 = [ a+(1/a) ]2 -2 = 25-2 =23
1/2*5+1/3*5+1/8*11+.+1/20*23=?
题目应该有误
1/2*5+1/8*5+1/8*11+......+1/20*23
=(1/2-1/5+1/5-1/8+1/8-1/11+......+1/20-1/23)/3
=(1/2-1/23)/3
=(21/46)/3
=7/46
1/1*3+1/3*5+1/5*7+.+1/23*25+1/25*27=?
1/1*3+1/3*5+1/5*7+......+1/23*25+1/25*27
=(1/2)*(1/1-1/3)+(1/2)*(1/3-1/5)+(1/2)*(1/5-1/7)+...+(1/2)*(1/25-1/27)
=(1/2)*(1/1-1/3+1/3-1/5+1/5-1/7+...+1/25-1/27)
=(1/2)*(1-1/27)
=(1/2)*(26/27)
=13/27.
