Finding the second derivative of $f(x) = \frac{4x}{x^2-4}$. What is the second derivative of 
$$f(x) = \frac{4x}{x^2-4}?$$ I have tried to use the quotient rule but I can't seem to get the answer.

As Jonh said, $f(x)=\frac{2}{x+2}+\frac{2}{x-2}$, and so, 
$f'(x)=\frac{-2}{(x+2)^2}+\frac{-2}{(x-2)^2}$, and
$f''(x)=\frac{4}{(x+2)^3}+\frac{4}{(x-2)^3}$.
