$1) \, y = \dfrac{1 - 3x}{2x + 1}$
$y$ xác định $\Leftrightarrow 2x + 1 \ne 0 \Leftrightarrow x \ne -\dfrac{1}{2}$
$\Rightarrow TXĐ: D = R\backslash\left\{-\dfrac{1}{2}\right\}$
$2) \, y = \dfrac{4}{11 - 5x}$
$y$ xác định $\Leftrightarrow 11 - 5x \ne 0 \Leftrightarrow x \ne \dfrac{11}{5}$
$\Rightarrow TXĐ: D = R\backslash\left\{\dfrac{11}{5}\right\}$
$3) \, y = -\dfrac{2}{x^2 - 3x + 2}$
$y$ xác định $\Leftrightarrow x^2 - 3x + 2 \ne 0 \Leftrightarrow \begin{cases}x \ne 1\\x \ne 2\end{cases}$
$\Rightarrow TXĐ: D = R \backslash\left\{1;2\right\}$
$4) \, y = \sqrt{3x - 5}$
$y$ xác định $\Leftrightarrow 3x - 5 \geq 0 \Leftrightarrow x \geq \dfrac{5}{3}$
$\Rightarrow TXĐ: D = \left[\dfrac{5}{3};+\infty\right)$
