cos(3π/2+α)=-3/5,α为第四象限角,求tan(2π-α)

cos(3π/2+α)=-3/5,α为第四象限角,求tan(2π-α)
cos(3π/2+α)=sinα=-3/5,α为第四象限角,故cosα=√(1-9/25)=4/5
∴tan(2π-α)=-tanα=-sinα/cosα=-(-3/5)/(4/5)=3/4