1. ## Confused about simple u substition problem for natural log

i'm trying to find the integral of 4/(6x+9). I let u be equal to 6x+9 and du be 6dx. Thus it is (4/6)lnu=(2/3)ln(6x+9). However my calculator says it is (2/3)ln(2x+3)...They are obviously different..What am i doing wrong?

2. Wait a minute... Are you sure thats what your calculator says? Because mine doesn't.

http://integrals.wolfram.com/index.j...9&random=false

3. Yeah..thats what my TI-89 and my teacher says it is...

4. Originally Posted by bfpri
Yeah..thats what my TI-89 and my teacher says it is...
There is no discrepancy. The two answers differ by a constant, so you can absorb it into the $+C$.

$\frac{2}{3}\ln(6x+9) = \frac{2}{3}\ln(2x+3)+\frac{2}{3}\ln(3)$