-2*x --------- 2 / 2 \ \x + 1/
(-2*x)/(x^2 + 1)^2
-2*x/(1 + x^2)^2
-2*x --------- 2 / 2\ \1 + x /
-2.0*x/(1.0 + x^2)^2
-2*x ------------- 4 2 1 + x + 2*x
-2*x/(1 + x^4 + 2*x^2)