1. $\sqrt{3} \tan 3x -3=0$
ĐKXĐ : $\cos 3x \ne 0$
$\Leftrightarrow 3x \ne \dfrac{\pi}{2} + k\pi \to x \ne \dfrac{\pi}{6} + \dfrac{k\pi}{3} (k \in \mathbb{Z})$
2. $\tan \Big(3x + \dfrac{\pi}{2} \Big). \cot \Big(5 x - \pi\Big) =1$
ĐKXĐ : $\cos \Big(3x + \dfrac{\pi}{2} \Big) \ne 0 , \sin \Big(5 x - \pi\Big) \ne 0$
$\to x \ne \dfrac{k\pi}{3}, x \ne \dfrac{k\pi}{5} (k \in \mathbb{Z}) $
3. $\cot (4x+2)^2 =-\sqrt{3}$
ĐKXĐ : $\sin (4x+2)^2 \ne 0$
$\to 4x +2 \ne k\pi$
$\to x \ne \dfrac{-1}{2} + \dfrac{k\pi}{4} (k \in \mathbb{Z}) $
4. $\cot (45°-x)=\dfrac{\sqrt{3}}{3}$
ĐKXĐ : $\sin (45°-x) \ne 0$
$\to 45°-x \ne k180°$
$\to x \ne 45° - k180° (k \in \mathbb{Z})$
