∫sectdt＝∫cost/(cost)^2dt
＝∫1/(cost)^2dsint
＝∫1/(1-(sint)^2)dsint
令sint = x化为∫1/(1-x^2)dx=(ln|1+x|-ln|1-x|)/2+C
=ln(根号((1+x)/(1-x)))+C
=ln|sect＋tant|＋C