y=1/cosx+√(2sinx+1)
cosx≠0且2sinx+1≥0
x≠kπ+π/2且2kπ-π/3≤x≤2kπ+4π/3(k∈Z)
即2kπ-π/6≤x≤2kπ+7π/6且x≠2kπ+π/2(k∈Z)