Cho hàm số

- Hướng dẫn giải

$$\begin{gathered} y \text{'} =\frac{(2x-4)(x+1)-(x^2-4x+1)}{{(x+1)}^2} \\ y \text{'} =\frac{x^2+2x-5}{{(x+1)}^2} \\ y \text{'} =0\iff x^2+2x-5=0 \\ \iff \left\{\begin{array}{l}{x}_1=-1+\sqrt{6}\\ x_2=-1-\sqrt{6}\end{array}\right. \\ \Rightarrow x_1{x}_2=-5 \end{gathered}$$