Hello, I need to factor 4x^4-5x^2-9 and I'm not sure how to do it.

The closest I got was:

(2x^2+3)(2x^2-3)-5X^2

but I wasn't sure what do do with the -5X^2. I also tried:

4x^4-5x^2-9

X^2(4x^2 -5)-3^2

But then I wasn't sure what to do with the 9. Can someone please direct me as to what I am doing wrong or how to do the problem? Thanks