2cosx+cos x-1=0 , x принадлежит [-7П/2 ; 2П)

Cosx=a
2a+a-1=0
D=1+8=9
a1=(-1-3)/4=-1cosa=-1a=+2n,nz
-7/2+2n2
-72+4n4
-94n2
-9/4n1/2
n=-2a=-4=-3
n=-1a=-2=-
n=0a=
a2=(-1+3)/4=1/2cosx=1/2x=/3+2k U x=-/3+2m
-7/2/3+2k2
-212+12k12
-2312k10
-23/12k5/6
k=-1a=/3-2=-5/3
k=0a=/3
-7/2-/3+2m2
-21-2+12m12
-1912m14
-19/12m7/6
m=-1a=-/3-2=-7/3
m=0a=-/3
m=1a=-/3+2=5/3