416. Calculate $\cos 300^{\circ}$.
Solution. Since $300^{\circ}=270^{\circ}+30^{\circ}$ and the given angle ends in the IV quadrant, then $\cos 300^{\circ}=\cos \left(270^{\circ}+30^{\circ}\right)=\sin 30^{\circ}=1 / 2$.