Đáp án:
a) $D=\Bbb R\backslash\left\{-\dfrac{\pi}{2} + k2\pi\,\Big| \, k \in\Bbb Z\right\}$
b) $D=\Bbb R\backslash\left\{\pi + k2\pi\,\Big| \, k \in\Bbb Z\right\}$
Giải thích các bước giải:
a) $y =\dfrac{2\cos x -1}{\sin x +1}$
$y$ xác định $\Leftrightarrow \sin x + 1 \ne 0$
$\Leftrightarrow \sin x \ne -1$
$\Leftrightarrow x \ne -\dfrac{\pi}{2} + k2\pi\quad (k\in\Bbb Z)$
$\Rightarrow TXD: D=\Bbb R\backslash\left\{-\dfrac{\pi}{2} + k2\pi\,\Big| \, k \in\Bbb Z\right\}$
b) $y =\dfrac{2\sin x -1}{\cos x +1}$
$y$ xác định $\Leftrightarrow \cos x + 1 \ne 0$
$\Leftrightarrow \cos x \ne -1$
$\Leftrightarrow x \ne \pi + k2\pi\quad (k\in\Bbb Z)$
$\Rightarrow TXD: D=\Bbb R\backslash\left\{\pi + k2\pi\,\Big| \, k \in\Bbb Z\right\}$
