TXĐ của: y= tanx/sinx – cosx

$y= \dfrac{\tan x}{\sin x – \cos x}$
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) $\Rightarrow\sin(x-\dfrac{\pi}{4})\ne0\Rightarrow x-\dfrac{\pi}{4}\ne k\pi$
$\Rightarrow x\ne\dfrac{\pi}{4}+k\pi$