hộ mình nhe mình cần gấp

Đáp án+Giải thích các bước giải:

Bài 2:

`a) 4(18 - 5x) - 12(3x - 7) = 15(2x - 16) - 6(x + 14)`

`72 - 20x - (36x - 84) = 30x - 240 - (6x + 84)`

`72 - 20x - 36x + 84 = 30x - 240 - 6x - 84`

`-20x - 36x - 30x + 6x = -240 - 84 - 72 - 84`

`-80x = -480`

`x = -480 : (-80)`

`x = 6`

Vậy `x ∈ {6}`.

`b) 5(3x + 5) - 4(2x - 3) = 5x + 3(2x + 12) + 1`

`15x + 25 - (8x - 12) = 5x + 6x + 36 + 1`

`15x + 25 - 8x + 12 = 5x + 6x + 36 + 1`

`15x - 8x - 5x - 6x = 36 + 1 - 25 - 12`

`-4x = 0` 

`x = 0 : (-4)`

`x = 0`

Vậy `x ∈ {0}`.

`c) 2(5x - 8) - 3(4x - 5) = 4(3x - 4) + 11`

`10x - 16 - (12x - 15) = 12x - 16 + 11`

`10x - 16 - 12x + 15 = 12x - 16 + 11`

`10x - 12x - 12x = -16 + 11 + 16 - 15`

`-14x = -4`

`x = -4 : (-14)`

`x = 2/7`

Vậy `x ∈ {2/7}`.

`d) 5x - 3{4x - 2[4x - 3(5x - 2)]} = 182`

`5x - 3{4x - 2[4x - 15x + 6]} = 182`

`5x - 3{4x - 8x + 30x - 12} = 182`

`5x - 12x + 24x - 90x + 36 = 182`

`5x - 12x + 24x - 90x = 182 - 36`

`-73x = 146`

`x = 146 : (-73)`

`x = -2`

Vậy `x ∈ {-2}`.

Bài 3:

`a) A = x^3 - 30x^2 - 31x + 1`

Tại `x = 31` nên ta có:

`A = 31^3 - 30. 31^2 - 31. 31 + 1`

`A = 29791 - 30. 961 - 961 + 1`

`A = 29791 - 28830 - 961 + 1`

`A = 1`.