由tan(A+B)=(tanA+tanB)/(1-tanAtanB)得
tan(α+45°)=（tanα+1）/（1-tanα)
tan(α-45°)=（tanα-1）/（1+tanα)
则tan(α+45°)+tan(α-45°)=（tanα+1）/（1-tanα)+（tanα-1）/（1+tanα)
=(（tanα+1）^2+(1-tanα)^2)/(1-tan^2α)
=2(1+tan^2 α)/(1-tan^2 α)能不能继续化简了上面化错了。。。减号写成加号了。。。tan(α+45°)+tan(α-45°)=（tanα+1）/（1-tanα)+（tanα-1）/（1+tanα)=(（tanα+1）^2-(1-tanα)^2)/(1-tan^2α)=4tanα/(1-tan^2 α) =2tan2α