ение \( -15 \cos \left(\frac{\pi}{2}+\alpha\right) \), если \( \cos \alpha=-\frac{7}{25} \) и \( \alpha \in\left(\frac{\pi}{2} ; \pi\right) \)

1) \( y=\cos 4 \theta \)

31.1.Agar \( \bar{a} \) va \( \bar{b} \) vektorlar uchun \( a \) ) \( \left.|\bar{a}|=4,|\bar{b}|=5, a=30^{\circ} ; b\right)|\bar{a}|=8,|\bar{b}|=7, a=45^{\circ} \); d) \( \left.|\bar{a}|=2.4,|\bar{b}|=10, \alpha=60^{\circ} ; e\right)|\bar{a}|=0,8, \left\lvert\, \bar{b}=\frac{1}{2}\right., a=40^{\circ} \) bo \( \mid \) sa, bu vektorlaming skal ko'paytmasini toping (bu yerda \( -\bar{a} \) va \( \bar{b} \) vektorlar orasidagi burchak).

8) \( y=3 \cot \frac{\theta}{2} \)

B1.1. Agar \( \bar{a} \) va \( \bar{b} \) vektorlar uchun \( a \) ) \( \left.|\bar{a}|=4,|\bar{b}|=5, a=30^{\circ} ; b\right)|\bar{a}|=8,|\bar{b}|=7, a=45^{\circ} \); a) \( \left.|\bar{a}|=2.4, \mid \bar{b}=10, a=60^{\circ} ; e\right)|\bar{a}|=0,8,|\bar{b}|=\frac{1}{2}, a=40^{\circ} \) bo'lsa, bu vektorlarning skalar ko'paytmasini toping (bu yerda \( -\bar{a} \) va \( \bar{b} \) vektorlar orasidagi burchak).

7) \( 5\left(\cos \frac{7 \pi}{6}+i \sin \frac{7 \pi}{6}\right) \)