K
Khách

Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.

4 tháng 10 2016

\(S=\frac{10}{56}+\frac{10}{140}+\frac{10}{260}+.......+\frac{10}{1400}\)

\(S=\frac{5}{28}+\frac{5}{70}+\frac{5}{130}+\frac{5}{700}\)

\(\frac{3S}{5}=\frac{3}{4}\times7+\frac{3}{7}\times10+\frac{30}{10}\times13+........+\frac{3}{25}\times28\)

\(\frac{3S}{5}=\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+......+\frac{1}{25}-\frac{1}{28}\)

\(\frac{3S}{5}=\frac{1}{4}-\frac{1}{28}\)

\(\frac{3S}{5}=\frac{3}{14}\)

\(S=\frac{3}{14}\times\frac{5}{3}\)

\(S=\frac{5}{14}\)

Vậy \(S=\frac{5}{14}\)

S=10/56+10/140+10/260+....+10/1400

S=5/28+5/70+5/130+....+5/700

3S/5=3/4.7+3/7.10+3/10.13+...+3/25.28

3S/5=1/4-1/7+1/7-1/10+1/10-1/13+....+1/25-1/28

3S/5=1/4-1/28

3S/5=3/14

S=3/14.5/3

S=5/14

Vậy S=5/14

16 tháng 4 2015

S=10/56+10/140+10/260+...........+10/1400

S=5/28+5/70+5/130+........+5/700

3S/5=3/4.7+3/7.10+3/13.10+.........+3/25.28

3S/5=1/4-1/7+1/7-1/10+1/10-1/13+.........+1/25-1/28

3S/5=1/4-1/28

3S/5=3/14

S=3/14.5/3

S=5/14

9 tháng 8 2016

S = 10/56 + 10/140 + 10/260 + ....... + 10/1400

S = 5/28 + 5/70 + 5/130 + 5/700

3S/5 = 3/4 x 7 + 3/7 x 10 + 30/10 x 13 + ....... + 3/25 x 28

3S/5 = 1/4 - 1/7 + 1/7 - 1/10 + 1/10 - 1/13 + ........ + 1/25 - 1/28

3S/5 = 1/4 - 1/28

3S/5 = 3/14

S = 3/14 x 5/3

S = 5/14

Vậy S = 5/14

9 tháng 8 2016

\(S=\frac{10}{56}+\frac{10}{140}+\frac{10}{260}+\frac{10}{1400}\)

\(S=\frac{5}{28}+\frac{5}{70}+\frac{5}{130}+...+\frac{5}{700}\)

\(S=\frac{5}{4.7}+\frac{5}{7.10}+\frac{5}{10.13}+...+\frac{5}{25.28}\)

\(S=5.\left(\frac{3}{4.7}+\frac{3}{7.10}+\frac{3}{10.13}+...+\frac{3}{25.28}\right)\)

\(S=5.\left(\frac{1}{4.7}+\frac{1}{7.10}+\frac{1}{10.13}+...+\frac{1}{25.28}\right)\)

\(S=5.\left(\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+...+\frac{1}{25}-\frac{1}{28}\right)\)

\(S=5.\left(\frac{1}{4}-\frac{1}{28}\right)\)

\(S=5.\frac{3}{14}=\frac{15}{14}\)

Vậy \(S=\frac{15}{14}\)

31 tháng 3 2019

S= 10/56+10/140+.....+10/1400

S= 5/28+5/70+.....+5/700

S= 5/4.7+5/7.10+......+5/25.28

S=5/3( 1/4-1/7+1/7-1/10+......+1/25-1/28)

S= 5/3.(1/4-1/28)

S= 5/3. 3/14

S= 15/42

VẬY S= 15/ 42

25 tháng 4 2016

Đặt S= 5/28 + 5/70 + 5/130 +.....+5/700

= 5/4.7 + 5/7.10 + ......+ 5/ 25.28

3S/5=1/4-1/7+1/7-1/10+.....+1/25-1/28

3S/5=1/4-1/28

3S/5=3/14

3S=3/14x5

3S=15/14

S=15/14x1/3

S=15/42

14 tháng 2 2016

M=10/56+10/140+10/260+...+10/1400

=5/28+5/70+5/130+...+5/700

=5/4.7+5/7.10+5/10.13+...+5/25.28

=5/3(3/4.7+3/7.10+3/10.13+...+3/25.28)

=5/3(1/4-1/7+1/7-1/10+1/10-1/1+...+1/25-1/28)

=5/3.(1/4-1/28)

=5/3.3/14

=5/14

14 tháng 2 2016

khó @gmail.com

\(A=\frac{10}{56}+\frac{10}{140}+\frac{10}{260}+...+\frac{10}{1400}\)

\(A=\frac{5}{28}+\frac{5}{70}+\frac{5}{130}+...+\frac{5}{700}\)

\(\frac{3A}{5}=\frac{3}{4\times7}+\frac{3}{7\times10}+\frac{3}{10\times13}+...+\frac{3}{25\times28}\)

\(\frac{3A}{5}=\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+...+\frac{1}{25}-\frac{1}{28}\)

\(\frac{3A}{5}=\frac{1}{4}-\frac{1}{28}\)

\(\frac{3A}{5}=\frac{3}{14}\)

\(A=\frac{3}{14}\times\frac{5}{3}\)

\(A=\frac{5}{14}\)

5 tháng 2 2022

undefined

@py. Hello, hihi

17 tháng 1 2016

M=5/28+5/70+...+5/700=5/4.7+5/7.10+...+5/25.28=>3M=5(1/4-1/7+1/7-1/10+...+1/25-1/28)

=>3M=5(1/4-1/28)=>3M=15/14=>M=5/14

6 tháng 3 2016

Đầu tiên rút gọn M trước 
M= 5/28 + 5/70 +.....+10/700 
= 5/(4.7)+5/(7.10)+....5/(25.28) 
3M= 5( 1/4 - 1/7 +1/7-1/10+......+1/25-1/28) 
3M= 5 (1/4-1/28) 
3M=15/14 
M= 5/14 :D