cos2α/tan(α+π/4)=
问题描述：
cos2α/tan(α+π/4)=
答
cos2α/tan(α+π/4)= (cos²α - sin²α) / [(tanα+1)/(1-tanα)]= cos²α (1-tan²α)/ [(tanα+1)/(1-tanα)]= cos²α (1-tan²α)(1-tanα)/ (1+tanα)= cos²α(1-tanα)²...