Hi! I would really appreciate any help solving couple of integrals. I probably wasted weeks on them... and small forest worth of paper...

1st should be solved with u-substitution;

$\displaystyle \int \frac{2^x\cdot 3^x}{9^x+4^x}dx$

$\displaystyle \int \frac{x^3-6}{x^4+6x+8}dx$

$\displaystyle \int \frac{\sqrt{2x-1}+\sqrt{4x-1}+1}{\sqrt{2x-1}-\sqrt{4x+1}}dx$

If anyone have any idea how to solve them, because they all appear unsolvable to me (or anyone I asked for help so far).