解：tana=2tan(a/2)/[1-tan²(a/2)] =-4/3所以tan(a+π/4） =(tana+tanπ/4)/(1-tanatanπ/4) =(-4/3+1)/(1+4/3) =-1/7
tan(a/2)=2∴tana=2tan(a/2)/[1-tan(a/2)^2]=-4/3∴tan(a+π/4)=(tana+1)/(1-tana)=-1/7
