Giúp mình gấp với ạ

`~rai~`

\(y=\cot2x\\ĐKXĐ:\sin2x\ne 0\\\Leftrightarrow 2x\ne k\pi\\\Leftrightarrow x\ne k\dfrac{\pi}{2}.(k\in\mathbb{Z})\\TXĐ:D=\mathbb{R}\backslash\left\{k\dfrac{\pi}{2}\Big|k\in\mathbb{Z}\right\}.\\\to\text{Chọn ý A.}\)