sin (x/2) > ✓3/2
(π/3)+2πn ≤ (x/2) ≤ (2π/3)+2πn, n ∈ Z см. рис. Умножаем на 2: [b](2π/3)+4πn ≤ x ≤ (4π/3)+4πn, n ∈ Z[/b]