f(x)=cos(13/2π-2x) =cos(6π+π/2 -2x)
= cos(π/2 -2x)=sin(2x),
2kπ-π/2≤2x≤2kπ+π/2,
kπ-π/4≤x≤kπ+π/4.(k∈Z)
所以函数的递增区间是[kπ-π/4,kπ+π/4] (k∈Z).