[latex]( \frac{x}{x^{2} -1} )'' [/latex]

[latex]f(x)= \frac{x}{x^2-1} [/latex] [latex]f'(x)= \frac{x^2-1-2x^2}{(x^2-1)^2} = \frac{-x^2-1}{(x^2-1)^2} [/latex] [latex]f''(x)=\frac{-2x(x^2-1)^2-4x(-x^2-1)(x^2-1)}{(x^2-1)^4} [/latex]