$\displaystyle \lim x \rightarrow \infty \dfrac{\sqrt{9x^{6} - x}}{x^{3} + 5}$

$\displaystyle \lim x \rightarrow \infty \dfrac{(9x^{6} - x)^{1/2}}{x^{3} + 5}$

Hint?

I know that infinity plugged into any $\displaystyle \dfrac{a}{n}$ (where n is a variable to any power) is zero.