$\displaystyle \displaystyle \int \frac{1}{x^2+12 x + 72}\,dx$

I don't know where to begin! Substitution definitely does not work. Integration by parts & partial fractions do not seem to work either.

I cannot factor the denominator. I get imaginary roots!

How do I proceed with this type of problem? Thanks. PS: I suspect it has something to do with the arctan function!

Thanks!