ʃxsecx²dx
=1/2ʃsecx²dx²
=1/2ln|tanx²/2|+C

OL(secx)^2=1+(tanx)^2

∫x(secx)^2dx＝∫x (secx)^2 dx＝ʃxdtanx =xtanx－∫tanxdx ＝xtanx＋ln|cosx|＋COK