tanα/2＝2tana=2tan(a/2)/(1-tan²(a/2))=2*2/(1-4)=-4/3tan(a-π/4)=(tana-1)/(1+tana)=(-7/3)/(-1/3)=7(3sinα+cosα)/(3cosα-sinα)=(3tana+1)/(3-tana)=(-3)/(13/3)=-9/13