Đáp án`+`Giải thích các bước giải:

 `a, (x - 2)(x - 3)(x + 1)(x + 2) = 60`

`<=> [(x - 2)(x + 1)][(x - 3)(x + 2)] = 60`

`<=> (x^2 + x - 2x - 2)(x^2 + 2x - 3x -6) = 60`

`<=> (x^2 -x - 2)(x^2 - x - 6) = 60`

`<=> (x^2 -x - 2)^2 - 4(x^2 - x - 2) -60 = 0`

`<=> (x^2 -x - 2)^2 -10(x^2 - x - 2) + 6(x^2 -x - 2)- 60 = 0`

`<=> (x^2 -x - 2)(x^2 -x- 2 - 10) + 6(x^2 -x - 2 - 10)=  0`

`<=> (x^2 -x - 12)(x^2 - x- 2 + 6) = 0`

`<=> (x^2 + 3x- 4x - 12)(x^2 -x + 4) = 0`

`<=> [x(x + 3) - 4(x + 3)](x^2 -x + 1/4 + (15)/4)= 0`

`<=> (x + 3)(x- 4) [(x- 1/2)^2+ (15)/4] = 0`

`<=> (x + 3)(x - 4) = 0` (do `(x - 1/2)^2 + (15)/4 > 0 AAx \in RR`)

`<=>` $\left[\begin{matrix} x=-3\\ x=4\end{matrix}\right.$

Vậy `S= {-3;4}`

`b, (x - 4)(x - 2)(x + 2)(x + 4) = 189`

`<=> [(x- 4)(x + 4)][(x - 2)(x + 2)] = 189`

`<=> (x^2 - 16)(x^2 - 4) = 189`

`<=> (x^2 - 4)^2 - 12(x^2 - 4) - 189 = 0`

`<=> (x^2- 4)^2 - 21(x^2 - 4) + 9(x^2 - 4) - 189 = 0`

`<=> (x^2 - 4)(x^2 - 4 - 21) + 9(x^2 - 4 - 21) = 0`

`<=> (x^2 - 25)(x^2- 4 + 9) = 0`

`<=> (x^2- 25)(x^2 + 5) = 0`

`<=> x^2 - 25= 0` (do `x^2 +5 >0 AAx \in RR`)`

<=> x = +-5`

Vậy `S= {+-5}`

`***`sharksosad