How do you integrate int 1/(t^3sqrt(t^2-1))1t3t21 by trigonometric substitution?

How do you integrate int 1/(t^3sqrt(t^2-1))dt1t3t21dt by trigonometric substitution?

1 Answer
Aug 31, 2016

1/2(arc sect+sqrt(t^2-1)/t^2)+C12(arcsect+t21t2)+C.

Explanation:

Let I=int1/(t^3sqrt(t^2-1))dtI=1t3t21dt.

We subst. t=sec x, "so that," dt=sec xtan xdxt=secx,so that,dt=secxtanxdx. Hence,

I=int(secxtanx)/(sec^3xtanx)dx=intcos^2xdx=int(1+cos2x)/2dxI=secxtanxsec3xtanxdx=cos2xdx=1+cos2x2dx

=1/2{x+(sin2x)/2}=1/2(x+sinxcos)=12{x+sin2x2}=12(x+sinxcos)

Now, secx=t rArr x=arc sect, cos x=1/t, sinx=sqrt(1-1/t^2)secx=tx=arcsect,cosx=1t,sinx=11t2.

Therefore, I=1/2{arc sect+(1/t)(sqrt(t^2-1)/t}I=12{arcsect+(1t)(t21t}, or,

I=1/2(arc sect+sqrt(t^2-1)/t^2)+CI=12(arcsect+t21t2)+C.

Enjoy Maths.!