$\begin{array}{l}a) \,\,y = \sqrt{x-2}\\ \text{y xác định}\,\Leftrightarrow x - 2 \geq 0 \Leftrightarrow x \geq 2\\ \Rightarrow TXĐ: D = [2;+\infty)\\ c)\,\,y = \dfrac{2x + 1}{x + 2}\\ \text{y xác định}\,\Leftrightarrow x + 2 > 0 \Leftrightarrow x > -2\\ \Rightarrow TXĐ: D = (-2;+\infty)\\ d)\,\,y = x + \dfrac{1}{\sqrt{3 - x}}\\ \text{y xác định}\,\Leftrightarrow \Leftrightarrow 3 - x > 0\Leftrightarrow x < 3\\ \Rightarrow TXĐ: D = (-\infty;3)\\ f) \,\,y = \sqrt{x ^2 + 2} + \sqrt x\\ \text{y xác định}\,\Leftrightarrow \begin{cases}x^2 + 2 \geq 0\\x \geq 0\end{cases}\\ \Leftrightarrow x \geq 0\\ \Rightarrow TXĐ: D = [0;+\infty)\\ h)\,\,y = \sqrt{2 + x} + \sqrt{x - 2}\\ \text{y xác định}\,\Leftrightarrow \begin{cases}2 + x \geq 0\\x - 2\geq 0 \end{cases}\\ \Leftrightarrow -2 \leq x \leq 2\\ \Rightarrow TXĐ: D = [-2;2]\end{array}$
