Đáp án`+`Giải thích các bước giải:

 `6, (3x - 2)^2 - (3x - 1)^2`

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

`= -1(6x - 3)`

`= 3 - 6x`

`9, (-2x + 3)^2 - (5x - 3)^2`

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

`= 3x(6 - 7x)`

`= 18x -2 1x^2`

`12, -(x + 1)^2 + (x - 1)^2`

`= (x - 1)^2 - (x + 1)^2`

`= (x - 1 -x - 1)(x- 1 + x + 1)`

`= -2.2x`

`= - 4x`

`15, -(2x + 7)^2 + (-2x - 3)^2`

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

`= (-2x - 3 - 2x - 7)(-2x - 3 + 2x + 7)`

`= 4(-4x - 10)`

`= -8(2x + 5)`

`= -16x - 40`

`13, (2x + 7)^2 + (-2x - 3)^2`

`= (2x + 7)^2 + (2x + 3)^2`

`= 4x^2 + 28x + 49 + 4x^2 + 12x + 9`

`= 8x^2 + 40x + 58`

`***`sharksosad