№4. Запишите формулы и вычислите: cos 150°, sin 150°, cos 120°, sin 120°, cos 135°, sin 135°.

Используем формулы приведения:

1. \(\cos 150^\circ=\cos(180^\circ-30^\circ)=-\cos 30^\circ=-\frac{\sqrt{3}}{2}\).
2. \(\sin 150^\circ=\sin(180^\circ-30^\circ)=\sin 30^\circ=\frac{1}{2}\).
3. \(\cos 120^\circ=\cos(180^\circ-60^\circ)=-\cos 60^\circ=-\frac{1}{2}\).
4. \(\sin 120^\circ=\sin(180^\circ-60^\circ)=\sin 60^\circ=\frac{\sqrt{3}}{2}\).
5. \(\cos 135^\circ=\cos(180^\circ-45^\circ)=-\cos 45^\circ=-\frac{\sqrt{2}}{2}\).
6. \(\sin 135^\circ=\sin(180^\circ-45^\circ)=\sin 45^\circ=\frac{\sqrt{2}}{2}\).

Ответ: \(\cos150^\circ=-\frac{\sqrt3}{2}\), \(\sin150^\circ=\frac12\), \(\cos120^\circ=-\frac12\), \(\sin120^\circ=\frac{\sqrt3}{2}\), \(\cos135^\circ=-\frac{\sqrt2}{2}\), \(\sin135^\circ=\frac{\sqrt2}{2}\).