cos(2x+π/6)> √2/2
-π/4+2πn≤2x+π/6≤π/4+2πn
-π/4-π/6+2πn ≤2x≤ π/4-π/6+2πn
-π/12+2πn≤ 2x≤ ≤π/12+2πn
-π/24+πn ≤ x ≤ π/24+πn , n∈Z
