Đáp án `+` Giải thích các bước giải:

`bb 6A.`

`a) - 2x(x + 3) + x(2x - 1) = 10 `

`−2x ^ 2 −6x+2x ^ 2 −x=10`

`(−2x^2+2x^2)+(−6x−x)=10`

`−7x=10`

`x = 10 : (-7)`

`x = -10/7`

Vậy `x = -10/7`

``

`b) (2/3 x)((9x)/2 + 1/4) - (3x ^ 2 + x + 2) = 3`

`3x^2 + 1/6x - 3x^2 - x - 2 = 3`

`(3x^2 - 3x^2) + (1/6x - x) - 2 = 3`

`-5/6x - 2 = 3`

`-5/6x = 5`

`x = 5 : (-5/6)`

`x = -6`

Vậy `x = -6`

``

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

`2x^2 + 8x + 3x + 12 + x^2 - 2x - 5x + 10 = 3x^ 2 +4x+22`

`(2x^2 + x^2) + (8x + 3x - 2x - 5x) + (12 + 10) = 3x ^ 2 −17x+20`

`3x^2 + 4x + 22 = 3x^2 - 17x + 20`

`3x^2 +4x + 22 - 3x^2 + 17x - 20 = 0`

`(3x^2 - 3x^2) + (4x + 17x) + (22 - 20) = 0`

`21x+ 2 = 0`

`21x = -2`

`x = -2 : 21`

`x = -2/21`

Vậy `x = -2/21`

``

`bb 6B.`

`a) 3x(x - 5) - x(3x - 7) = 16`

` 3x^2 - 15x - 3x^2 + 7x = 16`

` (3x^2 - 3x^2) + (-15x + 7x) = 16 `

` -8x = 16`

` x = -2`

Vậy `x = -2`

``

`b) - 2x ^ 2 + 3x + 6 + (5/7  x)((14x)/5 + 21) = 9`

` -2x^2 + 3x + 6 + 2x^2 + 15x = 9`

`(-2x^2 + 2x^2) + (3x + 15x) + 6 = 9 `

` 18x + 6 = 9 `

` 18x = 3 `

` x = 1/6`

Vậy `x = 1/6`

``

`c) (x + 1)(4x + 3) + (x + 2)(x + 3) = (5x - 1)(x - 1) + 28`

`4x^2 + 3x + 4x + 3 + x^2 + 3x + 2x + 6 = 5x^2 - 5x - x + 1 + 28`

`(4x^2 + x^2) + (3x +4x + 3x + 2x) + (3 + 6) = 5x^2 - 6x + 29`

`5x^2 + 12x + 9 = 5x^2 - 6x + 29`

`5x^2 + 12x - 5x^2 + 6x = - 9 + 29 `

` (5x^2 - 5x^2) + (12x + 6x) = 29 - 9`

` 18x = 20`

`x = 20: 18`

`x = 10/9` 

Vậy `x = 10/9`