tan（α+π/4）+tan（α-π/4）=2tan2α
问题描述：
tan（α+π/4）+tan（α-π/4）=2tan2α
求证、
答
tan(α+π/4)+tan(α-π/4)..用公式拆开=(tanα+tanπ/4)/(1-tanαtanπ/4)+(tanα-tanπ/4)/(1+tanαtanπ/4)..将tanπ/4写成1 =(1+tanα)/(1-tanα)+(tanα-1)/(1+tanα)=(1+tanα)/(1-tanα)-(1-tanα)/(tan...