## anonymous 4 years ago Need help on the next step of this definite integral

1. anonymous

$\int\limits_{1}^{2} 3x/\sqrt{4x+5} dx$ I used the u-sub of sqrt{4x+5}, u^2=4x+5 got 2udu=4dx and then udu=2dx. I feel like the next step is right in front of my eyes but I'm just not seeing it

2. anonymous

when you sub in for dx, the u will cancel with the sqrt(4x+5) since it is equal to u replace x with (u^2 -5)/4 $\rightarrow \frac{3}{8}\int\limits_{1}^{2}(u^{2}-5) du$

3. anonymous

Can I just pull the 3 out from the x like that?

4. anonymous

oh sorry i didn't see you responded yes you can, anytime it is a constant $\int\limits_{?}^{?}n*x dx= n \int\limits_{?}^{?}x dx$

5. anonymous

np, gave me time to try to figure it all out, lol.