chia ca hai ve cho $\sqrt2(\sqrt3-1)$ va dat $sin\alpha=\frac1{\sqrt2(\sqrt3-1)}; co s\alpha=\frac{\sqrt3-2}{\sqrt2(\sqrt3-1)}$
PT=>$sin3xsin\alpha+co s3xco s\alpha=sin\alpha=>co s(3x-\alpha)=co s(\frac{\pi}2-\alpha)$
$=>x=\frac{\pi}6+\frac k3\pi$ va x=........