![](https://rs.olm.vn/images/avt/0.png?1311)
Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
=1/1-1/4+1/4-1/7+1/7-1/10+1/10-1/13+1/13-1/16
=1-1/16=15/16
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
Ta có : \(\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+\frac{3}{10.13}+\frac{3}{13.16}\)
\(=1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+.......+\frac{1}{13}-\frac{1}{16}\)
\(=1-\frac{1}{16}\)
\(=\frac{15}{16}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a=511/256
b=647/20
c=mình đang suy nghĩ,nhưng nếu bạn k cho mình thì bạn sẽ có câu trả lời
a. 1 + 1/2 + 1/4 + 1/8 + 1/16 + 1/32 + 1/64 + 1/128 + 1/256
= 1 + ( 1 - 1/2) + ( 1/2 - 1/4) + ( 1/4 - 1/8) + ( 1/8 - 1/16) + ( 1/16 - 1/32) + (1/32 - 1/64) + ( 1/64 - 1/128) + (1/128 - 1/256)
= 1 + 1 - 1/2 + 1/2 - 1/4 + 1/4 - 1/8 + 1/8 - 1/16 + 1/16 - 1/32 + 1/32 - 1/64 + 1/64 - 1/128 + 1/128 - 1/256
= 2 - 1/256
= 511/256
Câu b bạn có viết sai đề không vậy?
![](https://rs.olm.vn/images/avt/0.png?1311)
Ta có :
1/1.4+1/4.7+...+1/91.94
=1/3.(1/1-1/4+...+1/91-1/94)
=1/3.(1/1-1/94)
=1/3.93/94
=31/94
Ta có :
1/1.4+1/4.7+...+1/91.94
=1/3.(1/1-1/4+...+1/91-1/94)
=1/3.(1/1-1/94)
=1/3.93/94
=31/94
Tính nhanh
a) 5/1x3 + 5/3x5 + 5/5x7 + ........ + 5/43x45
b) 6/1x4 + 6/4x7 + 6/7x10 + ...... + 6/97x100
![](https://rs.olm.vn/images/avt/0.png?1311)
\(a,\frac{5}{1.3}+\frac{5}{3.5}+\frac{5}{5.7}+...+\frac{5}{43.45}=\frac{5}{2}\left(\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5.7}+...+\frac{2}{43.45}\right)=\frac{5}{3}\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{43}-\frac{1}{45}\right)=\frac{5}{3}.\frac{44}{45}=\frac{44}{27}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
x + 21/40 = 53/40
x = 53/40 - 21/40
x = 32/40 = 4/5
34/35 : x = 17/5
x = 34/35 : 17/5
x = 2/7
`x + 3 / 4 xx 7 / 10 = 53 / 40`
`x + 21 / 40 = 53 / 40`
`x = 53 / 40 - 21 / 40`
`x = 32 / 40`
`x = 4 / 5`
____________________________
`( 2 / 5 + 4 / 7 ) : x = 17 / 5`
`( 14 / 35 + 20 / 35 ) : x = 17 / 5`
`34 / 35 : x = 17 / 5`
`x = 34 / 35 : 17 / 5`
`x = 34 / 35 xx 5 / 17`
`x = 2 / 7`
![](https://rs.olm.vn/images/avt/0.png?1311)
Bài 1
a 2/5+3/6=12/30+15/30=27/30=9/10 .
b 5/9-1/6=30/54-9/54=21/54=7/18
![](https://rs.olm.vn/images/avt/0.png?1311)
A ) 3: 5/7 = 3/1 :5/7 = 3/1 x 7/5 = 21/5
B) 4: 1/3 = 4/1 : 1/3 = 4/1 x 3/1 = 12/1 = 12
C) 5 : 1/6 = 5/1 :1/6 = 5/1 x 6/1 = 30 /1 =30
Đúng 100000000000% luôn , chúc bạn học tốt ^_^
ta có :
\(\frac{3}{1\times4}+\frac{4}{4\times7}+..+\frac{3}{100\times103}=1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+..+\frac{1}{100}-\frac{1}{103}\)
\(=1-\frac{1}{103}=\frac{102}{103}\)