Áp dụng công thức: \(\sin x = \alpha ⇔ x=\left[ \begin{array}{l}x=\alpha +k2\pi\\x=\pi-\alpha + k2\pi \end{array} \right.\)
$⇒ \sin x \ne \dfrac12 $
\(⇔\begin{cases}x\ne \dfrac{\pi}{6} +k2\pi\\x\ne \pi-\dfrac{\pi}{6} + k2\pi\end{cases}\)
\(⇔\begin{cases}x\ne \dfrac{\pi}{6} +k2\pi\\x\ne \dfrac{5\pi}6 + k2\pi\end{cases} \ (k \in \mathbb{Z})\)