tan(α+π/4)=(tanα+tanπ/4)/(1-tanα*tanπ/4)=(tanα+1)/(1-tanα)=-1/7解得tanα=-4/3（cos2α+1）/【2cos(α-π/4)*sin(α+π/4)-sin2α】=2cos²α/[sin2α+sin(π/2)-sin2α]=2/(1+tan²α)=2/[1+(-...