tan(a+π/4)
=(tana+tan(π/4))/[1-tana *tan(π/4)]
=(3+1)/(1-3*1)
=-2
tan(a-π/4)
=(tana-tan(π/4))/[1+tana *tan(π/4)]
=(3-1)/(1+3)
=2/4
=1/2
不懂的欢迎追问,