Để \(f\left(x\right)>0\) \(\forall x\Leftrightarrow\left\{{}\begin{matrix}m^2-1=0\\m+1>0\end{matrix}\right.\) \(\Rightarrow m=1\)
\(\left(m-1\right)\left(m+1\right)x+m+1>0\)
\(\Leftrightarrow\left(m-1\right)\left(m+1\right)x>-\left(m+1\right)\)
Xét m=-1
\(\Rightarrow0.\left(-2\right).x>0\left(l\right)\)
Xét \(m=1\Rightarrow0.2x>-2\left(lđ \forall x\right)\)
Xét \(m\ne\pm1\Rightarrow x>\frac{-1}{m-1}\)