
两角和的正切公式:
tan(A+B)=(tanA+tanB)/(1-tanAtanB)
三角函数值:tanπ/4=1
tan(a+π/4)
=(tan a+tan π/4)/(1-tan a tan π/4)
=(tan a+1)/(1-tan a)=(3+1)/(1-3)=-2

两角和的正切公式:
tan(A+B)=(tanA+tanB)/(1-tanAtanB)
三角函数值:tanπ/4=1
tan(a+π/4)
=(tan a+tan π/4)/(1-tan a tan π/4)
=(tan a+1)/(1-tan a)=(3+1)/(1-3)=-2