371. Calculate: a) $\sin 110^{\circ}$; b) $\operatorname{tg} 945^{\circ}$; c) $\cos \frac{25 \pi}{4}$.
Solution. a) The period of the function $y=\sin x$ is $360^{\circ}$; therefore, we can omit the integer number of periods:

$$
\sin 1110^{\circ}=\sin \left(360^{\circ} \cdot 3+30^{\circ}\right)=\sin 30^{\circ}=\frac{1}{2}
$$

b) Since the period of the function $y=\operatorname{tg} x$ is $180^{\circ}$, then

$$
\operatorname{tg} 945^{\circ}=\operatorname{tg}\left(180^{\circ} \cdot 5+45^{\circ}\right)=\operatorname{tg} 45^{\circ}=1
$$

c) We find

$$
\cos \frac{25 \pi}{4}=\cos 6 \frac{1}{4} \pi=\cos \left(6 \pi+\frac{\pi}{4}\right)=\cos \frac{\pi}{4}=\frac{\sqrt{2}}{2} .
$$

372-374. Calculate the values of the functions of the following angles: