Along with many other things (namely, finding concavity, increasing/decreasing, inflection, etc.), my teacher assigned to me to find any horizontal asymptotes by using limits at infinity. The function I was given is y = |x^4-9x^2|. I am not exactly certain how to do this sort of thing with absolute value. I end up with

|infinity^4 - 9infinity^2|, and isn't this some sort of indeterminant form?