tana=2tan(a/2)/(1-tan^2(a/2))=4/(1-4)=-4/3
所以
tan(a+pi/4)=(1-4/3)/(1+4/3)=-1/7
（6sina+cosa）/（3sina-2cosa）=(6tana+1)/(3tana-2)=(-8+1)/(-4-2)=7/6