4sin2xcos2x меньше равно под корнем 2
2sin4x≤√2 sin4x≤√2/2 3π/4+2πn≤4x≤9π/4+2πn 3π/16+πn/2≤x≤9π/16+πn/2 x∈[3π/16+πn/2;9π/16+πn/2,n∈z]