[Ne[S]zA]

ข้อ3)
$$\frac{\sin \theta}{\cos \theta}(1-\sin \theta)=\frac{2(1-2\sin^2\theta)}{\cos \theta}$$
$$\sin \theta -\sin^2\theta=2-4\sin^2\theta$$
$$3\sin^2\theta+\sin \theta -2=0$$
$$(3\sin -2)(\sin \theta +1)=0$$
$$\sin \theta =\frac{2}{3},-1$$
$$\frac{2}{3}-1=-\frac{1}{3}$$