`1/3^(2x+2) + 1/3^(2x-1) + 1/3^(2x-2) = 109/729`
` => 1/(3^(2x) . 3^2) + 1/(3^(2x) : 3) + 1/(3^(2x) : 3^2) = 109/729`
`=> 1/(3^(2x) . 3^2) + 1/(3^(2x) .1/3 ) + 1/(3^(2x) .1/3^2) = 109/729`
`=> 1/3^(2x) . 1/(3^2) + 1/3^(2x) . 1/(1/3) + 1/3^(2x) . 1/(1/3^2) =109/729`
`=> 1/3^(2x) . 1/9 + 1/3^(2x) . 3 + 1/3^(2x) . 9 =109/729`
`=> 1/3^(2x) . (1/9 + 3 + 9) = 109/729`
`=> 1/3^(2x) . 109/9 = 109/729`
`=> 1/3^(2x) = 109/729 : 109/9`
`=> 1/3^(2x) = 1/81`
`=> 1/3^(2x) = 1/3^4 `
`=> 2x =4`
`=> x = 2`
Vậy `x=2` là giá trị cần tìm
