y=sin(x-π/3)cosx=[sin(2x-π/3)+sin(-π/3)]/2

这是积化和差公式：
sinαcosβ=[sin(α+β)+sin(α-β)]/2
还有
sinαsinβ=-[cos(α+β)-cos(α-β)]/2
cosαcosβ=[cos(α+β)+cos(α-β)]/2