√2/2sinx-√2/2cosx>=-1/2
Sin(x-π/4)≥-1/2 -π/6+2πk≤x-π/4≤7π/6+2πk -π/6+π/4+2πk≤x≤7π/6+π/4+2πk π/12+2πk≤x≤17π/12+2πk,k∈z