Đáp án:
`1/9+(1-1/3^2018)/8`
Giải thích các bước giải:
`1/9+1/9+1/81+1/729+...+1/3^2018`
`=1/9+(1/9+1/81+1/729+...+1/3^2018)`
Đặt `A= 1/9+1/81+1/729+...+1/3^2018`
`A=1/3^2+1/3^4+1/3^6+...+1/3^2018`
`3^2A=1+1/3^2+1/3^4+....+1/3^2016`
`9A-A=8A=1-1/3^2018`
`A=(1-1/3^2018)/8`
`=1/9+A=1/9+(1-1/3^2018)/8`
