Chapter 2.5, Problem 45E

Horizontal asymptotes Determine $\underset{x\to \infty }{\lim }f\left(x\right)$ and $\underset{x\to -\infty }{\lim }f\left(x\right)$ for the following functions Then give the horizontal asymptotes of f (if any).

45.     $f\left(x\right)=\frac{1}{2x^4-\sqrt{4x^8-9x^4}}$