Ta có: \(3{\sin}^2 x+4\cos x-2=0\)
\(\Leftrightarrow 3(1-{\cos}^2 x)+4\cos x-2=0\)
\(\Leftrightarrow 3{\cos}^2 x-4\cos x-1=0\)
\(\Leftrightarrow \left[ \begin{array}{l} \cos x=\dfrac{2-\sqrt{7}}{3}\\\cos x=\dfrac{2+\sqrt{7}}{3}>1\text{(loại)}\end{array} \right. \)
\(\Leftrightarrow x=\pm\arccos{\left({\dfrac{2-\sqrt{7}}{3}}\right)}+k2\pi,k\in\mathbb{Z}\).
