Answer:
x = {0, π/3, π, 4π/3}
Step-by-step explanation:
4cos⁴(x) - 5cos²(x) + 1 = 0
(u² - 1)(4u² - 1) = 0
u² - 1 = 0
u² = 1
u = ± 1
cos x = ± 1
=> x = 0 or π
4u² - 1 = 0
4u² = 1
u² = 1/4
u = ± 1/2
cos x = ± 1/2
=> x = π/3 or 4π/3
Therefore, x = {0, π/3, π, 4π/3}.
