7-7cos²x+8cosx-8=0
7cos²x-8cosx+1=0
cosx=t
7t²-8t+1=0
D=64-28=36
t1=(8-6)/14=1/7⇒cosx=1/7⇒x=+-arccos1/7+2πk,k∈z
t2=(8+6)/14=1⇒cosx=1⇒x=2πn,n∈z
1)x=-arccos1/7 U x=arccos1/7
2)x=0
Х^2-0,04х^2+0,2х+0,01=0
0,96х^2+0,2х+0,01=0
96x^2+20x+1=0
D=b^2-4ac=400-384=16
x1=-1/8
x2=-1/12
А)=10-5а-12а-4=6-17а
б)=1.1-1.1х+1.2+1.2х=2.3+0.1х
в)=18б-54+18б+6=36б-48