(sin x - 0.5) · (cos x + 0.4) = 0
1) sin x - 0.5 = 0
sin x = 0.5
x₁ = π/6 +2πk k ∈ Z
x₂ = 5π/6 +2πn n ∈ Z
2) cos x + 0.4 = 0
cos x = -0.4
x₃ = π - arc cos 0.4 + 2πm m ∈ Z
x₄ = -π + arc cos 0.4 + 2πr r ∈ Z
