`~rai~`
\(8)y=tan\left(-2x+\dfrac{\pi}{6}\right)\\ĐKXĐ:cos\left(-2x+\dfrac{\pi}{6}\right)\ne 0\\\Leftrightarrow -2x+\dfrac{\pi}{6}\ne \dfrac{\pi}{2}+k\pi\\\Leftrightarrow -2x\ne \dfrac{\pi}{3}+k\pi\\\Leftrightarrow x\ne -\dfrac{\pi}{6}-k\dfrac{\pi}{2}.(k\in\mathbb{Z})\\\Rightarrow D=\mathbb{R}\backslash\left\{-\dfrac{\pi}{6}-k\dfrac{\pi}{2};k\in\mathbb{Z}\right\}.\\9)cot\left(\dfrac{x}{2}-\dfrac{\pi}{4}\right)\\ĐKXĐ:sin\left(\dfrac{x}{2}-\dfrac{\pi}{4}\right)\ne 0\\\Leftrightarrow \dfrac{x}{2}-\dfrac{\pi}{4}\ne k\pi\\\Leftrightarrow \dfrac{x}{2}\ne \dfrac{\pi}{4}+k\pi\\\Leftrightarrow x\ne\dfrac{\pi}{2}+k2\pi.(k\in\mathbb{Z})\\\Rightarrow D=\mathbb{R}\backslash\left\{\dfrac{\pi}{2}+k2\pi;k\in\mathbb{Z}\right\}.\\10)\dfrac{cosx}{cos^2x-sin^2x}\\ĐKXĐ:cos^2x-sin^2x\ne 0\\\Leftrightarrow cos2x\ne 0\\\Leftrightarrow 2x\ne \dfrac{\pi}{2}+k\pi\\\Leftrightarrow x\ne \dfrac{\pi}{4}+k\dfrac{\pi}{2}.(k\in\mathbb{Z})\\\Rightarrow D=\mathbb{R}\backslash\left\{\dfrac{\pi}{4}+k\dfrac{\pi}{2};k\in\mathbb{Z}\right\}.\)
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