y=cos(π/3-x/2),x∈[-2π,2π]
=cos(x/2-π/3)
由2kπ-π≤x/2-π/3≤2kπ,k∈Z
得2kπ-2π/3≤x/2≤2kπ+π/3,k∈Z
∴4kπ-4π/3≤x≤4kπ+2π/3,k∈Z
∵x∈[-2π,2π]
∴递增区间有：
[-4π/3,2π/3]