Answer:
x = pi, 3pi, 5pi etc
x = -pi, -3pi, -5pi etc
Step-by-step explanation:
cos^2 x + 2 cos x + 1 = 0
replace cos x with m
m^2 + 2m +1 = 0
solve by factoring (this is a^2 +2ab+b^2 = (a+b)^2 where a =m and b=1)
(m+1)^2=0
take the square root of each side
m+1 =0
m=-1
now replace m with cos x
cos x = -1
take arccos of each side
arccos cos x = arccos (-1)
x = pi, 3pi, 5pi etc
