1)y=根号下2cosx-1
2cosx-1≥0 cosx≥1/2 2nπ+π/3≥x≥2nπ-π/3 (n=1,2,3,...)
2)y=lg(3-4sin^2x)
3-4sin^2x>0 sin^2xsinx>-√3/2
所以 nπ-π/3