\(A=\left(\dfrac{x+1}{x-1}-\dfrac{x+1}{x-1}\right):\dfrac{x+2}{x^2-1}\)
\(a,ĐKXĐ:x^2-1\ne0\)
\(\Rightarrow\left[{}\begin{matrix}x-1\ne0\\x+1\ne0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x\ne1\\x\ne-1\end{matrix}\right.\)
\(b,RG\)
\(A=\left(\dfrac{x+1}{x-1}-\dfrac{x+1}{x-1}\right):\dfrac{x+2}{x^2-1}\)
\(\Leftrightarrow A=\dfrac{0}{\dfrac{x+2}{x^2-1}}=0\)