1. = 1- (2sint·cost·sint) / 2cost = 1-sin²t=cos²t
2 a) 7 ·(1-cos²х)+8cosx-8=0
7 - 7cos²х+8cosx-8=0
- 7cos²х+8cosx-1=0
cosx=t
-7t²+8t-1=0
D=64-4·(-7)·(-1)=36
x1=(-8+6 )/(-7)·2=-2/(-14)=1/7 cosx=1/7 ⇒ x=+- arccos 1/7 +2πn, n∈Z
х2=(-8-6 )/(-7)·2=-14/(-14)=1 cosx=1 ⇒ х=2πn, n∈Z
б) x=0, x=+- arccos 1/7