# Math Help - Indefinite Integral

1. ## Indefinite Integral

I've tried this so many times and I can't seem to find the right answer, please help.

2. All you need to set it is $u=\sqrt{36x^2-1}.$

3. What would du be in that case?

4. $du=\frac{36x}{\sqrt{36x^2-1}}\,dx.$