>>615
tan(x/2+π/4)
=(tan(π/4)+tan(x/2))/(1-tan(π/4)tan(x/2))
=(1+tan(x/2))/(1-tan(x/2))
=(cos(x/2)+sin(x/2))/(cos(x/2)-sin(x/2))
分子分母に　cos(x/2)+sin(x/2) を掛けて、倍角の公式を適用
=(1+sin(x))/cos(x)