In my homework for this week I have a question:

If I do a substitution

*u=3x+25*, then I have

Which does not help much.

If I try to find such

*u* that du will eliminate x from numerator, then:

*du=1/x dx* and

*u *have to be

*ln(x)*Which is also not very helpful...

Finally I run the original integral through Maxima, and it gave me:

Which is very scary and I have no idea how it come to this formula.

So which "u" should I use? How to find such "u"? Or maybe there is another approach I should use? I am completely stuck.