ĐK tự làm
PT $\Leftrightarrow \sin^2 x -3\cos^2 x = 4\sin x \cos x (\sin x + \sqrt 3 \cos x)$
$\Leftrightarrow (\sin x +\sqrt 3 \cos x)(\sin x -\sqrt 3 \cos x) -4\sin x \cos x (\sin x + \sqrt 3 \cos x)=0$
$\Leftrightarrow (\sin x + \sqrt 3 \cos x) \bigg [ \sin x -\sqrt 3 \cos x -2\sin 2x \bigg ] =0$ quá dễ rồi