Question

\(\dfrac{1}{4.7}\) +\(\dfrac{1}{7.10}\) +\(\dfrac{1}{10.13}\) +..........+\(\dfrac{1}{25.28}\)

. là dấu nhân đó nha

ai đúng cho tik nè

Answer 1

\(\dfrac{1}{4.7}+\dfrac{1}{7.10}+\dfrac{1}{10.13}+...+\dfrac{1}{25.28}\)
\(=\dfrac{1}{3}\left(\dfrac{3}{4.7}+\dfrac{3}{7.10}+\dfrac{3}{10.13}+...+\dfrac{3}{25.28}\right)\)
\(=\dfrac{1}{3}\left(\dfrac{1}{4}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{10}+\dfrac{1}{10}-\dfrac{1}{13}+...+\dfrac{1}{25}-\dfrac{1}{28}\right)\)
\(=\dfrac{1}{3}\left(\dfrac{1}{4}-\dfrac{1}{28}\right)\)
\(=\dfrac{1}{3}\cdot\dfrac{3}{14}\)
\(=\dfrac{1}{14}\)
#NoSimp

Answer 2

29/28

 

Answer 3

sai rồi nha lmc1

Answer 4

\(\dfrac{1}{14}\)?

Answer 5

=1/4 - 1/7 + 1/7 - 1/10 + 1/10 - 1/13 +...+ 1/15 - 1/28

= 1/4 - 1/28

= 3/24