最值得绝对值=1/2
A〉0,所以A=1/2
紧挨着的一对最大最小之间是半个周期
T/2=4π/9-π/9=π/3
T=2π/3
|w|=2π/T
w>0
所以w=3
y=1/2sin(3x+b)
x=π/9,y=1/2
sin(π/3+b)=1=sin(π/2)
b=π/6
y=1/2sin(3x+π/6)