Question

Solve. 4cos²x + 4cosx + 1= 0

Answer 1

let u = cosx
4u^2 + 4u + 1 = 0
(2u+1)(2u+1)
2u + 1 = 0
2u = -1
u = -1/2
cosx = -1/2
arc cosine it to get x

Answer 2

4cos²x + 4cosx + 1= 0
(2cosx+1)^2=0
(2cosx+1)=0
2cosx=-1
cosx = -1/2
x=120 degree or x=240 degree