1) $y = \dfrac{2 - x}{x^2 - 4x}$
$y$ xác định $\Leftrightarrow x^2 - 4x \ne 0\Leftrightarrow \begin{cases}x \ne 0\\x \ne 4\end{cases}$
$\Rightarrow TXĐ: D = \Bbb R \backslash\left\{0;4\right\}$
2) $y = \sqrt{1 + 2x} + \sqrt{6 + x}$
$y$ xác định $\Leftrightarrow \begin{cases}1 + 2x\geq 0\\6 + x \geq 0\end{cases}$
$\Leftrightarrow \begin{cases}x \geq -\dfrac{1}{2}\\x \geq -6\end{cases}$
$\Leftrightarrow x \geq - \dfrac{1}{2}$
$\Rightarrow TXĐ: D=\left[-\dfrac{1}{2};+\infty\right)$
