Question

Tính dãy quy luật sau:

s_6:10/56+10/140+10/28+....................+10/1400

giải giúp mk với

Answer 1

Sai đề hay sao ik

Answer 2

s_6:10/56+10/140+10/28+....................+10/1400

\(S_6=\frac{5}{28}+\frac{5}{70}+...+\frac{5}{700}\)

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

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

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

\(=\frac{5}{3}\cdot\frac{6}{28}\)

\(=\frac{15}{14}\)

Answer 3

s 10/56+10/140+10/28+....................+10/1400   S6 = + +. . . + 5 28 5 70 5 700 = + +. . . + 5 4.7 5 7.10 5 25.28 = ( − + − +. . . + − ) 5 3 1 4 1 7 1 7 1 10 1 25 1 28 = ( − ) 5 3 1 4 1 28 = ⋅ 5 3 6 28 = 15 14