`~rai~`
\(y=2021x^2+\tan\left(x+\dfrac{\pi}{4}\right)\\ĐKXĐ:\cos\left(x+\dfrac{\pi}{4}\right)\ne 0\\\Leftrightarrow x+\dfrac{\pi}{4}\ne\dfrac{\pi}{2}+k\pi\\\Leftrightarrow x\ne\dfrac{\pi}{4}+k\pi.(k\in\mathbb{Z})\\TXĐ:D=\mathbb{R}\backslash\left\{\dfrac{\pi}{4}+k\pi\Big|k\in\mathbb{Z}\right\}.\)
