`~rai~`
\(y=\dfrac{2\tan x+2}{(\cos x-1)(\sin^2x+1)}\\ĐKXĐ:\begin{cases}\cos x\ne0\\(\cos x-1)(\sin^2x+1)\ne 0\end{cases}\\\Leftrightarrow \begin{cases}x\ne \dfrac{\pi}{2}+k\pi\\\cos x-1\ne 0\quad\text{(do }\sin^2x+1\ge 1\quad\forall x)\end{cases}\\\Leftrightarrow \begin{cases}x\ne \dfrac{\pi}{2}+k\pi\\\cos x\ne 1\end{cases}\\\Leftrightarrow \begin{cases}x\ne \dfrac{\pi}{2}+k\pi\\x\ne k2\pi.\end{cases}\quad(k\in\mathbb{Z})\\TXĐ:D=\mathbb{R}\backslash\left\{\dfrac{\pi}{2}+k\pi;k2\pi\Big|k\in\mathbb{Z}\right\}.\)
