tan(α+π/4)=-3/5
(tanα+1)/(1-tanα)=-3/5
tanα=-4
tan(α-π/4)=(tanα-1)/(1+tanα)=5/3
tan(α-π/4)=-cot(α-π/4+π/2)=-cot(α+π/4)=-1/tan(α+π/4)=5/3