∫ x/(1+cosx) dx=∫ x/[2cos²(x/2)] dx=∫ xsec²(x/2) d(x/2)=∫ x dtan(x/2)分部积分=xtan(x/2) - ∫ tan(x/2) dx=xtan(x/2) - 2∫ sin(x/2)/cos(x/2) d(x/2)=xtan(x/2) + 2∫ 1/cos(x/2) dcos(x/2)=xta...