sin(α)cos(β)=12[sin(α+β)+sin(α−β)]=−12[cos(α+β)−sin(α−β)] \sin(\alpha)\cos(\beta)=\dfrac{1}{2}\left[\sin(\alpha+\beta)+\sin(\alpha-\beta)\right]=-\dfrac{1}{2}\left[\cos(\alpha+\beta)-\sin(\alpha-\beta)\right] sin(α)cos(β)=21[sin(α+β)+sin(α−β)]=−21[cos(α+β)−sin(α−β)]
cos(α)cos(β)=12[sin(α+β)−sin(α−β)]=12[cos(α+β)+cos(α−β)] \cos(\alpha)\cos(\beta)=\dfrac{1}{2}\left[\sin(\alpha+\beta)-\sin(\alpha-\beta)\right]=\dfrac{1}{2}\left[\cos(\alpha+\beta)+\cos(\alpha-\beta)\right] cos(α)cos(β)=21[sin(α+β)−sin(α−β)]=21[cos(α+β)+cos(α−β)]
