1+tanx/1-tanx=2012
左边,分子分母同乘以cosx
(cosx+sinx)/(cosx-sinx)=2012
左边,分子分母同乘以cosx+sinx
(cosx+sinx)²/(cos²x-sin²x)=2012
(1+sin2x)/cos2x=2012
1/cos2x+tan2x=2012