How do you evaluate the integral int x"arcsec"(x^2)xarcsec(x2)?

1 Answer
May 20, 2018

int x*arcsec(x^2)*dxxarcsec(x2)dx

=1/2x^2*arcsec(x^2)-1/2ln(x^2+sqrt(x^4-1))+C12x2arcsec(x2)12ln(x2+x41)+C

Explanation:

int x*arcsec(x^2)*dxxarcsec(x2)dx

=1/2int 2x*arcsec(x^2)*dx122xarcsec(x2)dx

After using y=x^2y=x2 and 2x*dx=dy2xdx=dy transforms, this integral became

1/2int arcsecy*dy12arcsecydy

After using z=arcsecyz=arcsecy, y=seczy=secz and dy=secz*tanz*dzdy=secztanzdz transforms, it became

1/2int z*secz*tanz*dz12zsecztanzdz

=1/2z*secz-1/2int secz*dz12zsecz12seczdz

=1/2z*secz-1/2int (secz*(secz+tanz)*dz)/(secz+tanz)12zsecz12secz(secz+tanz)dzsecz+tanz

=1/2z*secz-1/2ln(secz+tanz)+C12zsecz12ln(secz+tanz)+C

For y=seczy=secz, tanztanz must be equal to sqrt(y^2-1)y21. Thus,

1/2y*arcsecy-1/2ln(y+sqrt(y^2-1))+C12yarcsecy12ln(y+y21)+C

=1/2x^2*arcsec(x^2)-1/2ln(x^2+sqrt(x^4-1))+C12x2arcsec(x2)12ln(x2+x41)+C