List all x intercepts for y = - cos (1/2x + 1/5 pi) on the interval [-2/5pi, 4pi]

- cos (1/2 x + 1/5 π) = 0 (and because if cos α = 0, α = π/2 + k π, k ∈ Z)

1/2 x + π/5 = π/2 + k π, k ∈ Z

1/2 x = π/2 - π/5 + k π / * 2

x = π - 2π/5 + 2 k π

x = 3/5 π + 2 k π = 0.6 π + 2 k π

Answer:

If k = 0: x 1 = 0.6 π = 3π/5

k = 1 : x 2 = 2.6 π = 13π/5