`~rai~`
\(y=\dfrac{\tan2x}{1-\tan x}\\ĐKXĐ:\begin{cases}\cos2x\ne 0\\1-\tan x\ne 0\end{cases}\\\Leftrightarrow \begin{cases}2x\ne \dfrac{\pi}{2}+k\pi\\\tan x\ne 1\end{cases}\\\Leftrightarrow \begin{cases}x\ne \dfrac{\pi}{4}+k\dfrac{\pi}{2}\\x\ne \dfrac{\pi}{4}+k\pi\end{cases}\\\Leftrightarrow x\ne \dfrac{\pi}{4}+k\dfrac{\pi}{2}.(k\in\mathbb{Z})\\TXĐ:D=\mathbb{R}\backslash\left\{\dfrac{\pi}{4}+k\dfrac{\pi}{2}\Big|k\in\mathbb{Z}\right\}.\)
