Question

Calculus 2nd order derivative

f(x)= 1/(x^2-1)

f ' = -2x/(x^2-1)^2

I have worked it out to
-2(x^2-1)^2 - 4x(x^2-1)x over
(x^2-1)^4

I don't see how to arrive at the answer of
6x^2+2 over
(x^2-1)^4

any help is appreciated.