2 câu trả lời
$y= \dfrac{\tan x}{\sin x - \cos x}$ Đk: $\left\{ \begin{array}{l} \cos x\ne 0 \\ \sin x - \cos x\ne0 \end{array} \right .$ $\Rightarrow \left\{ \begin{array}{l} x\ne\pm\dfrac{\pi}{2}+k2\pi \\ \sqrt2\sin( x - \dfrac{\pi}{4})\ne0 (1)\end{array} \right .$ (1) $\Rightarrow\sin(x-\dfrac{\pi}{4})\ne0\Rightarrow x-\dfrac{\pi}{4}\ne k\pi$ $\Rightarrow x\ne\dfrac{\pi}{4}+k\pi$
