f(α)=cot（-α-π）sin（-π-α）分之(sin(π-α)cos(2π+α)tan(-α+3π/2))?

f(α)=[sin(π-α)cos(2π+α)tan(-α+3π/2)]/cot（-α-π）sin（-π-α）
=sinαcosαcotα/(-cotαsinα)=-cosα
cos(α-3π/2)=1/5=-sinα,sinα=-1/5,cosα=-2√6/5 ,f(α)=-cosα=-2√6/5