公式1~6均为诱导公式,公式5、6可以实现正弦函数与余弦函数的相互转化
sin(α+k·2Π)=sin α
cos(α+k·2Π)=cos α
tan(α+k·2Π)=tan α
sin(Π+α)=-sin α
cos(Π+α)=-cos α
tan(Π+α)=tan α
sin(-α)=-sin α
cos(-α)=cos α
tan(-α)=-tan α
sin(Π-α)=sin α
cos(Π-α)=-cos α
tan(Π-α)=-tan α
sin(Π/2-α)=cos α
cos(Π/2-α)=sin α
sin(Π/2+α)=cos α
cos(Π/2+α)=-sin α