Question

Tổng 1/ 1.2 + 1/ 2.3 + ... + 1/ 9.10 bằng

Answer 1

\(=1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+...+\dfrac{1}{9}-\dfrac{1}{10}\)

\(=1-\dfrac{1}{10}=\dfrac{10}{10}-\dfrac{1}{10}=\dfrac{9}{10}\)

Answer 2

9/10

Answer 3

= 1 - 1/2 + 1/2 -1/3 + ... + 1/9 - 1/10

= 1 - 1/10

= 9/10