4sin2xcoc2x>или= корень 2

4sin2x*cos2x ≥ √22(2sin2x*cos2x) ≥ √22*sin4x ≥ √2sin4x ≥ √2/2π/4+2πn ≤ 4x ≤ 3π/4+2πn, n∈Zπ/16+πn/2 ≤ x ≤ 3π/16 +πn/2, n∈Zx∈[π/16+πn/2; 3π/16 +πn/2], n∈Z