tanx/2求不定积分
问题描述：
tanx/2求不定积分
答
∫tan(x/2) dx
= 2∫sin(x/2)/cos(x/2) d(x/2)
= -2∫1/cos(x/2) d[cos(x/2)]
= -2ln|cos(x/2)| + C
= 2ln|sec(x/2)| + C