Chọn câu sai A. 16x4(x – y) – x + y = (2x – 1)(2x + 1)(4x2 + 1)(x – y

* Hướng dẫn giải

$$\begin{gathered} +) 16x^4(x – y) – x + y \\ = 16x^4(x – y) – (x – y) \\ = (16x^4 – 1\left)\right(x – y) \\ = [{\left(2x\right)}^4 – 1\left]\right(x – y) \\ = [{\left(2x\right)}^2 – 1\left]\right[{\left(2x\right)}^2 + 1\left]\right(x – y) \\ = (2x – 1\left)\right(2x + 1\left)\right(4x^2 + 1\left)\right(x – y) \\ +) 16x^3 – 54y^3 \\ = 2(8x^3 – 27y^3) \\ = 2[{\left(2x\right)}^3 – {\left(3y\right)}^3] \\ = 2(2x – 3y)[{\left(2x\right)}^2 + 2x.3y + {\left(3y\right)}^2] \\ = 2(2x – 3y)(4x^2 + 6xy + 9y^2) \end{gathered}$$

Vậy A, B, D đúng. C sai

Đáp án cần chọn là: C