tan(π/4+θ）=(tanπ/4+tanθ)/(1-tanθtanπ/4) =(1+tanθ)/(1-tanθ)tan（π/4-θ）=(tanπ/4-tanθ)/(1+tanθtanπ/4)=(1-tanθ)/(1+tanθ)主要利用公式 tan（a+b)=(tana+tanb)/(1-tanata...