4сos^4x - 4cos^2x +1 = 0

Question

4сos^4x - 4cos^2x +1 = 0

Answer 1

4сos^4 x - 4cos^2 x +1 = 0
(2cos^2 x-1)^2=0
cos^2 x=1/2
cos x = √2/2
x=+-π/4+2πN
cosx=-√2/2
x=(π+-π/4)+2πN  (x=3π/4+2πN x=5π/4+πN)