Đáp án+Giải thích các bước giải:

`a)` `(x - 2)^2 - (x - 3)(x + 3) = 6`

`=>(x^2 - 4x + 4) - (x^2 - 9) = 6`

`=>x^2 - 4x + 4 - x^2 + 9 = 6`

`=>-4x + 13 = 6`

`=>-4x = 6 - 13`

`=>-4x = -7`

`=>x = 7/4`

`\text{Vậy}` `x=7/4`

`b)` `(x + 4)^2 - (1 - x)(1 + x) = 7`

`=>(x^2 + 8x + 16) - (1 - x^2) = 7`

`=>x^2 + 8x + 16 - 1 + x^2 = 7`

`=>2x^2 + 8x + 15 = 7`

`=>2x^2 + 8x + 15 - 7 = 0`

`=>2x^2 + 8x + 8 = 0`

`=>2(x^2 + 4x + 4) = 0`

`=>2(x + 2)^2 = 0`

`=>(x + 2)^2 = 0`

`=>x + 2 = 0`

`=>x = -2`

`c)` `(x - 4)^2 - (x - 2)(x + 2) = 6`

`=>(x^2 - 8x + 16) - (x^2 - 4) = 6`

`=>x^2 - 8x + 16 - x^2 + 4 = 6`

`=>-8x + 20 = 6`

`=>-8x = 6 - 20`

`=>-8x = -14`

`=>x = -14 / -8`

`=>x = 7/4`

`\text{Vậy}` `x=7/4`

`d)` `-4(x - 1)^2 + (2x - 1)(2x + 1) = -3`

`=>-4(x^2 - 2x + 1) + ( (2x)^2 - 1^2 ) = -3`

`=>-4x^2 + 8x - 4 + 4x^2 - 1 = -3`

`=>8x - 5 = -3`

`=>8x = -3 + 5`

`=>8x = 2`

`=>x = 2/8`

`=>x = 1/4`

`\text{Vậy}` `x=1/4`

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