Question

Tính tổng:

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

Answer 1

ai k mình thì nói cho mình biết để mình k lại

Answer 2

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

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

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

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

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

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

Answer 3

Dat A=10/56+10/140+.....+10/1400

=> A=5/28+5/70+.....+5/700

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

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

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

3A=5/3.3/14

3A=5/14

A=5/13:3

A=5/39