已知向量a=(sinx/3,cosx/3),向量b=(cosx/3,根号3 cosx/30 ,函数f(x)=向量a*b

1) f(x)=a*b=sin(x/3)*cos(x/3)+cos(x/3)*√3cos(x/3)=2cos(x/3)[1/2sin(x/3)+√3/2cos(x/3)]=2cos(x/3)sin(x/3+π/3)=sin(x/3+x/3+π/3)-sin(x/3-x/3-π/3)=sin(2x/3+π/3)+sin(π/3)=sin(2x/3+π/3)+√3/2图像对称...=2cos(x/3)sin(x/3+π/3) =sin(x/3+x/3+π/3)-sin(x/3-x/3-π/3)怎么算三角公式的积化和差公式：2cosαsinβ=sin(α+β)-sin(α-β)