∫1/sin(x/2)dx
=2∫csc(x/2)d(x/2)
=2∫sin(x/2)/(sin(x/2)^2)d(x/2)
=-2∫dcos(x/2)/(1-(cos(x/2))^2)
=ln|(1-cos(x/2))/(1+cos(x/2))|
=2ln|csc(x/2)-cot(x/2)|+C