`6cos^2 x + 5sin x - 2 = 0`
`<=> 6(1 - sin^2 x) + 5sin x - 2 = 0`
`<=> 6 - 6sin^2 x + 5sin x - 2 = 0`
`<=>` \(\left[ \begin{array}{l}sin x = \dfrac{4}{3} (l)\\sin x = -\dfrac{1}{2}\end{array} \right.\)
`<=>` \(\left[ \begin{array}{l}x = -\dfrac{\pi}{6} + k2\pi\\x = \dfrac{7\pi}{6} + k2\pi\end{array} \right.\) `(k in ZZ)`