Question

2/1*3 + 2/3*5 + 2/5*7 + .......+ 2/2019*2020

Mọi người giải giúp mình bài này nhá

Answer 1

=>S=2(1-1/3+1/3-1/4+....................-1/2020)

=>S=2*(1-1/2020)

=>s=2* 2019/2020

=>S=2019/1010

Answer 2

\(\frac{2}{1\cdot3}+\frac{2}{3\cdot5}+\frac{2}{5\cdot7}+...+\frac{2}{2017\cdot2019}+\frac{2}{2019\cdot2021}\)

\(=1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{2017}-\frac{1}{2019}+\frac{1}{2019}-\frac{1}{2021}\)

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

Answer 3

\(\frac{2}{1\times3}+\frac{2}{3\times5}+\frac{2}{5\times7}+...+\frac{2}{2019\times2021}\)

\(=1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{2019}-\frac{1}{2021}\)

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

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

Answer 4

Ta có :

\(\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5.7}+...+\frac{2}{2019.2021}\)

\(=1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+....+\frac{1}{2019}-\frac{1}{2021}\)

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

chúc bn học tốt!

Answer 5

Trả lời

\(\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5.7}+...+\)\(\frac{2}{2019.2020}\)

\(=1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{2019}-\frac{1}{2020}\)

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

Answer 6

\(\frac{2}{1\times3}+\frac{2}{3\times5}+...+\frac{2}{2019\times2021}\)

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

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