$3sinx-4sin^{3}x +4cos^{3}x -3cosx -sinx+cosx =\sqrt{2}\times(cos^{2}x-sin^{2}x)$$(cosx-sinx)\times (4cos^{2}x+4sin^{2}x+4sinxcosx -2-\sqrt{2}cosx-\sqrt{2}sinx) =0$
$(cosx-sinx)\times (2+4sinxcosx -sqrt{2}cosx-\sqrt{2}sinx) =0$
suy ra:cosx =sinx hoặc $2+4sinxcosx -sqrt{2}cosx-\sqrt{2}sinx) =0$