x∈(-π,-π/2)
x/3∈(-π/3,-π/6)
x/3+π/3∈(0,π/6)
y∈(0,1/2)答案好像是（0，1）x/3+π/3∈(0,π/6) sin(x/3+π/3)∈(0,1/2) 2sin(x/3+π/3)∈(0,1)