`~rai~`
\(\sin^23x=1\\\Leftrightarrow \dfrac{1-\cos6x}{2}=1\\\Leftrightarrow 1-\cos6x=2\\\Leftrightarrow \cos6x=-1\\\Leftrightarrow 6x=\pi+k2\pi\\\Leftrightarrow x=\dfrac{\pi}{6}+k\dfrac{\pi}{3}.(k\in\mathbb{Z})\\\text{Vậy S=}\left\{\dfrac{\pi}{6}+k\dfrac{\pi}{3}\Big|k\in\mathbb{Z}\right\}.\\c)\tan^22x=3\quad(1)\\ĐKXĐ:\cos^22x\ne 0\\\Leftrightarrow \cos2x\ne 0\\\Leftrightarrow 2x\ne\dfrac{\pi}{2}+k\pi\\\Leftrightarrow x\ne\dfrac{\pi}{4}+k\dfrac{\pi}{2}.(k\in\mathbb{Z})\\(1)\Leftrightarrow \dfrac{1-\cos4x}{1+\cos4x}=3\\\Leftrightarrow 1-\cos4x=3(1+\cos4x)\\\Leftrightarrow 1-\cos4x=3+3\cos4x\\\Leftrightarrow 4\cos4x=-2\\\Leftrightarrow \cos4x=-\dfrac{1}{2}\\\Leftrightarrow 4x=\pm\dfrac{2\pi}{3}+k2\pi\\\Leftrightarrow x=\pm\dfrac{\pi}{6}+k\dfrac{\pi}{2}.(k\in\mathbb{Z})\\\text{Vậy S=}\left\{\pm\dfrac{\pi}{6}+k\dfrac{\pi}{2}\Big|k\in\mathbb{Z}\right\}.\)
