VERO O FALSO?
a. Se $\cos \alpha=\sqrt{3} \sin \alpha, \operatorname{con} \pi<\alpha<\frac{3}{2} \pi$, allora $\sin \alpha=-\frac{1}{2}$.
b. Se $\cos x=\cos \frac{\pi}{6}$, allora $x=\frac{\pi}{6}$.
c. $\operatorname{Se} \sin \alpha=\frac{4}{5}$, allora $\cos \alpha=\frac{3}{5}$.
d. Se $\cos \alpha=\frac{1}{3}, \operatorname{con} 0<\alpha<\frac{\pi}{2}$, allora $\cos \alpha=\frac{\sqrt{2}}{4} \sin \alpha$.
