sec tdt 1+x 2 1+tan t (令x=tan = sector -Insect+tant+C =n|x+√1+x2|+C 原式= 1+x2 arctan x-ln|x+Ⅵ1+x2|+C′dx x  + 2 1 1 tdt t  + = 2 2 sec 1 tan 1 (令x=tant) tdt  = sec =ln|sect+tant|+C = ln | x + 1+ x | +C 2 ∴原式= 1+ x arctan x − ln | x + 1+ x | +C 2 2