因为tan(a-β)=(tana-tanβ)/(1+tanatanβ)=(2+1/3)/(1-2/3)=7
2、
因为tan(a+β)=(tana+tanβ)/(1-tanatanβ)=(2-1/3)/(1+2/3)=1
又0＜a＜π/2 ,π/2＜β＜π
所以π/2