tan(α+π/4)=1/3,即(tanα+tanπ/4)/(1-tanαtanπ/4)=1/3,(tanα+1)/(1-tanα)=1/3,所以tanα=-1/2.1 /（sinαcosα）=(sin²α+cos²α)/(sinαcosα)分子分母同除以cos²α可得：=(tan²α+1)/(tanα)=-5/2.
