Integration with Inverse Trig: Simplifying with Substitution

[crm08]

Homework Statement

$$\int\frac{dx}{9x^{2}+1}$$

Homework Equations

$$\frac{d}{dx}(arctan(x))$$ = $$\frac{1}{1+x^{2}}$$

The Attempt at a Solution

The other problems in this homework set all use the substitution rule but I can't find anything that would simplify the problem, my other guess would be to pull a (1/9) out, but then that would result in having a denominator = (x^2 + (1/9)), could someone get me on the right track, I have a feeling that I'm overlooking something obvious

 

[rootX]

Try u = 3x