Question

[thao jenny_006]

2/1.3+2/3.5+...+2/2019.2021

Hua se tk cho ban nhanh nhat (trc 12h trua)

Answer 1

[Trần Thanh Phương]

\(A=1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+...+\frac{1}{2019}-\frac{1}{2021}\)

\(A=1-\frac{1}{2021}\)

\(A=\frac{2020}{2021}\)

Answer 2

[Phạm Tuấn Đạt]

\(\frac{2}{1.3}+\frac{2}{3.5}+...+\frac{2}{2019.2021}\)

\(=1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+...+\frac{1}{2019}-\frac{1}{2021}\)

\(=1-\frac{1}{2021}=\frac{2020}{2021}\)