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