ĐK: $2\sin(2x+\dfrac{\pi}{6})-1\neq 0$
$\Leftrightarrow \sin(2x+\dfrac{\pi}{6})\neq \dfrac{1}{2}$
$\Leftrightarrow 2x+\dfrac{\pi}{6}\neq \dfrac{\pi}{6}+k2\pi$
hoặc $2x+\dfrac{\pi}{6}\neq \dfrac{5\pi}{6}+k2\pi$
$\Rightarrow D=\mathbb{R}$ \$\{k\pi; \dfrac{\pi}{3}+k\pi\}$