y=3sin(x+π/9)+5sin(x+4π/9)=3sin(x+π/9)+5sin(x+π/9+π/3)=3sin(x+π/9)+5/2*sin(x+π/9)+(5√3)/2*cos(x+π/9)=11/2*sin(x+π/9)+(5√3)/2*cos(x+π/9) （辅助角公式）=7sin(x+π/9+θ)故最大值是7...