ĐK $\cos x \ne 0$
Pt $\Leftrightarrow 5\sin x \cos^2 x -2\cos^2 x= 3(1-\sin x)\sin^2 x$
$\Leftrightarrow 5\sin x (1-\sin^2 x) -2(1-\sin^2 x) =3\sin^2 x -3\sin^3 x$
$\Leftrightarrow 2\sin^3 x +\sin^2 x -5\sin x +2=0$
$\Leftrightarrow (\sin x -1)(\sin x +2)(2\sin x -1)=0$ dễ rồi nhé