Điều kiện xác định: $x \neq 1$

$A = \dfrac{3x}{x - 1} - \dfrac{4}{2(x - 1)} + \dfrac{x}{-(x - 1)}$

$A = \dfrac{3x}{x - 1} - \dfrac{4}{2(x - 1)} - \dfrac{x}{x - 1}$

​$A = \dfrac{3x \cdot 2}{2(x - 1)} - \dfrac{4}{2(x - 1)} - \dfrac{x \cdot 2}{2(x - 1)}$

$A = \dfrac{6x - 4 - 2x}{2(x - 1)}$

$A = \dfrac{4x - 4}{2(x - 1)}$

$A = \dfrac{4(x - 1)}{2(x - 1)}$

$\Rightarrow A = \dfrac{4}{2} = 2$