Yes, it does look promising.

Thank you very much.]]>

You have multiplied by 3 instead of dividing by 3 when making the substitution...

]]>And after substituting back

But now if I differentiate it back:

Where did 9 come from?]]>

Continuing on the first thing you tried:

Can you continue from here?

]]>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.

]]>