tan(α-β)
=(tanα-tanβ)/(1+tanαtanβ)
=(7/3)/(1/3)
=7
0＜α＜π/2
π/2＜β＜π
π/2＜α+β＜3π/2
tan(α+β) = (tanα+tanβ)/(1-tanαAtanβ)
=[2+(-1/3)]/[1-(-1/3)*2]
=1
所以α+β=5π/4