I got f'(x)=[(x^2-4)^2(20)-2(x^2-4)(2x)(20x)]/(x^2-4)^4

=(-80x^4+340x^2-80)/(x^2-4)^3

and simplify

But I am pretty sure my first step was wrong, like I did the chain or product rule wrong because my answer does not match up to what my TI-89 says it is supposed to be.