ĐK: $\sin x\ne 0\to x\ne k\pi$
$\dfrac{\cos2x-3\cos x+2}{\sin x}=0$
$\to 2\cos^2x-1-3\cos x+2=0$
$\to 2\cos^2x-3\cos x+1=0$
$\to \left[ \begin{array}{l}\cos x=1\\ \cos x=\dfrac{1}{2}\end{array} \right.$
$\to \left[ \begin{array}{l}x=k2\pi \\x=\pm\dfrac{\pi}{3}+k2\pi\end{array} \right.$
Đối chiếu ĐK: $x\ne k\pi\to \begin{cases} x\ne k2\pi \\ x\ne \pi+k2\pi\end{cases}$
Vậy $x=\pm\dfrac{\pi}{3}+k2\pi$
