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