`color{#528B8B}{#A} color{#79CDCD}{n} color{#8DEEEE}{a} color{#97FFFF}{x} color{#BBFFFF}{a} color{#AFEEEE}{~}`

Đáp án `+` Giải thích các bước giải:

Đặt `A = 1/3+1/9+1/27+1/81+1/243+1/729 `

`A xx 3 = 3 xx (1/3 + 1/9 + 1/27 + 1/81 + 1/243 + 1/729)`

`A xx 3 = 1 + 1/3 + 1/9 + 1/27 + 1/81 + 1/243`

`A xx 3 = A + 3 - 1/243`

`A xx 2 = 3 - 1/243`

`A xx 2 = 728/243`

`A = 728/243 : 2`

`A = 364/243`

Vậy `1/3+1/9+1/27+1/81+1/243+1/729 = 364/243`