f(x)=Sin(2x/3+π/3)+√3/2
(-π/2+3kπ,√3/2)k∈Z
CosB=(a^2+c^2-b^2)/2ac≥(2ac-b^2)/2ac=1/2,即B∈(0,π/3]
f(x)∈[Sin(5π/9)+√3/2,√3)