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

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

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

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

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

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

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

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

B= 5/28 + 5/70 +.....+10/700 
= 5/(4.7)+5/(7.10)+....5/(25.28) 
3B= 5( 1/4 - 1/7 +1/7-1/10+......+1/25-1/28) 
3B = 5 (1/4-1/28) 
3B=15/14 
B = 15/14 : 3 

B = 5/14

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

S = 5 / 4x7 + 5 / 7x10 + 5 / 10x13 + ..... + 5 / 25x28

SX3 / 5 = 3 / 4x7 + 3 / 7x10 + ....... + 3 / 25x28

Sx3/5=1/4-1/7+1/7-1/10+1/10+.....+1/25-1/28

Sx3/5=1/4+(1/7-1/7)+(1/9-1/9)+.....+(!/25-1/25)-1/28

Sx3/5=1/4-1/28

Sx3/5=3/14

S = 3/14: 3/5

S = 5/14

Vậy S = 5 /14

tk mk nhé !

\(C=\frac{10}{56}+\frac{10}{140}+\frac{10}{260}+...+\frac{10}{1400}=10\left(\frac{1}{56}+\frac{1}{140}+\frac{1}{260}+...+\frac{10}{1400}\right)\)

\(C=\frac{10}{2}\left(\frac{1}{28}+\frac{1}{70}+\frac{1}{130}+...+\frac{1}{700}\right)=5\left(\frac{1}{4\cdot7}+\frac{1}{7\cdot10}+\frac{1}{10\cdot13}+...+\frac{1}{25\cdot28}\right)\)

\(C=5\cdot\frac{1}{3}\left(\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+...+\frac{1}{25}-\frac{1}{28}\right)\)

\(C=\frac{5}{3}\cdot\left(\frac{1}{4}-\frac{1}{28}\right)=\frac{5}{3}\cdot\frac{3}{14}=\frac{5}{14}\)

\(C=\frac{5}{28}+\frac{5}{70}+\frac{5}{130}+...+\frac{5}{700}=5\left(\frac{1}{4.7}+\frac{1}{7.10}+...+\frac{1}{25.28}\right)=\frac{5}{3}.\left(\frac{1}{4}-\frac{1}{28}\right)=\frac{5}{14}\)

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

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

3S/5 = 3/4 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

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

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

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

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

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

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

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

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

Vậy \(S=\frac{15}{14}\)

thank 2 bạn nha!

Doãn Hải Anh mk lớp 7 nên quên òi 

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

H=10/56+10/1400

H=13/70

vay H=13/70

ai di qua nho h cho minh nhe

SAO MÀ DỐT THẾ ! DỄ THẾ NÀY MÀ LÀM KHÔNG ĐƯỢC

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

H = 5/3 × (3/28 + 3/70 + 3/130 + ... + 3/700)

H = 5/3 × (3/4×7 + 3/7×10 + 3/10×13 + ... + 3/25×28)

H = 5/3 × (1/4 - 1/7 + 1/7 - 1/10 + 1/10 - 1/13 + ... + 1/25 - 1/28)

H = 5/3 × (1/4 - 1/28)

H = 5/3 × 3/14

H = 5/14

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

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

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

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

     \(=\frac{5}{3}.\left(\frac{1}{4}-\frac{1}{28}\right)\)

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

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

\(=\frac{5}{3}\times\left(\frac{3}{28}+\frac{3}{70}+....+\frac{3}{700}\right)\)

\(=\frac{5}{3}\times\left(\frac{3}{4}\times7+\frac{3}{7}\times10+.....+\frac{3}{25}\times28\right)\)

\(=\frac{5}{3}\times\left(\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-....+\frac{1}{25}-\frac{1}{28}\right)\)

\(=\frac{5}{3}\times\left(\frac{1}{4}-\frac{1}{28}\right)\)

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