1) cosx = 1/2
x = arccos(1/2) + 2πn, n ∈ Z
x = π/3 + 2πn, n ∈ Z.
2) cosx = -√2/2
x = ±arccos(-√2/2) + 2πn, n ∈ Z.
x = ±3π/4 + 2πn, n ∈ Z.
3) cosx = -√3/2
x = ±arccos(-√3/2) + 2πn, n ∈ Z
x = ±5π/6 + 2πn, n ∈ Z.
4) cosx = √3/2
x = arccos(√3/2) + 2πn, n ∈ Z
x = π/6 + 2πn, n ∈ Z.
5) cosx = -0,3
x = ±arccos(-0,3) + 3πn, n ∈ Z.