b, (1-x-1/x+1)(x+2)=x+1/x-1+x-1/x+1

* Hướng dẫn giải

$\left\{\begin{array}{l}x+1\ne 0\\ x-1\ne 0\end{array}\right.\Rightarrow x\ne \pm 1$

Ta có:

$$\begin{gathered} (1-\frac{x-1}{x+1})(x+2)=\frac{x+1}{x-1}+\frac{x-1}{x+1} \\ \iff \frac{2(x+2)}{x+1}=\frac{{\left(x+1\right)}^2+{\left(x-1\right)}^2}{x^2-1} \\ \iff \frac{2(x+2)\left(x-1\right)}{x^2-1}=\frac{2x^2+2}{x^2-1} \end{gathered}$$