Question

Tính tổng: M=10/56+10/140+10/260+...+10/1400

Answer 1

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

Answer 2

khó @gmail.com

Answer 3

\(\frac{5}{14}\)   Là đúng đó bn 

nhớ k cho mình nha! hjhj

Answer 4

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