a, đk : x khác -1 ; 1
\(=\dfrac{\left(3x-1\right)\left(x-1\right)-\left(2x+1\right)\left(x+1\right)}{\left(x-1\right)\left(x+1\right)}=\dfrac{3x^2-4x+1-2x^2-3x-1}{\left(x-1\right)\left(x+1\right)}\)
\(=\dfrac{x^2-7x}{\left(x-1\right)\left(x+1\right)}=\dfrac{x\left(x-7\right)}{\left(x-1\right)\left(x+1\right)}\)