Đáp án: `-6/11`

Lời giải:

`1/3x + 2/5(x+1) = 0`

    `=> 1/3x + 2/5x + 2/5 = 0`

    `=> x.(1/3+2/5) +2/5 = 0`

    `=> x.(1.5/3.5 + 2.3/5.3) + 2/5 = 0`

    `=> x.(5/15 + 6/15) + 2/5 = 0`

    `=> x . 11/15 + 2/5 = 0`

    `=> x . 11/15 = -2/5`

    `=> x = -2/5 : 11/15`

    `=> x = -2.15/11.5`

    `=> x = - 6/11`