积化和差sinαsinβ = [cos(α-β)-cos(α+β)] /2 cosαcosβ = [cos(α+β)+cos(α-β)]/2 sinαcosβ = [sin(α+β)+sin(α-β)]/2 cosαsinβ = [sin(α+β)-sin(α-β)]/2-2sin(B-C)cos(B+C)= -2[sin(B-C...