\(1+\frac13+\frac16+\cdots+\frac{2}{x\left(x+1\right)}=\frac{4040}{2021}\)
=>\(\frac22+\frac26+\frac{2}{12}+\cdots+\frac{2}{x\left(x+1\right)}=\frac{4040}{2021}\)
=>\(\frac12+\frac16+\cdots+\frac{1}{x\left(x+1\right)}=\frac{2020}{2021}\)
=>\(1-\frac12+\frac12-\frac13+\cdots+\frac{1}{x}-\frac{1}{x+1}=\frac{2020}{2021}\)
=>\(1-\frac{1}{x+1}=\frac{2020}{2021}\)
=>\(\frac{1}{x+1}=1-\frac{2020}{2021}=\frac{1}{2021}\)
=>x+1=2021
=>x=2020
Đúng 0
Bình luận (0)
