Question

[Chí Tiến]

1/2+1/6+1/12+1/20+...+1/x.[x+1]=2008/2009

Answer 1

[đăng việt cường]

=>1- 1/2 + 1/2 - 1/3+.....+1/x - 1/(x+1) = 2008/2009

=>1 - 1/(x+1) = 2008/2009

=>1 - 1/(x+1) =1-1/1009

=>1/(x+1)=1/2009

=>x+1=2009

=>x=2008.Vậy x=2008