2*sin(π/12)*(sin(π/6))积化和差：=cos(π/12)-cos(3*π/12)积化和差公式sinαsinβ=-[cos(α+β)-cos(α-β)]/2cosαcosβ=[cos(α+β)+cos(α-β)]/2sinαcosβ=[sin(α+β)+sin(α-β)]/2cosαsinβ=[sin(α+β...