Question

sin（α-2π）怎么算还有cos（α-2π）,tan（α-2π）,我只会算2π-α,倒过来就不知道怎么变号了

Answer 1

sin(α-2π)=sin(-2π+α)=sin[-(2π-α)]=-sin(2π-α)=sinα

cos(α-2π)=cos(-2π+α)=cos[-(2π-α)]=cos(2π-α)=cosα

tan(α-2π)=tan(-2π+α)=tan[-(2π-α)]=-tan(2π-α)=tanα