2 x - 1 ------ 2 x + 1
(x^2 - 1)/(x^2 + 1)
1 - 2/(1 + x^2)
2 1 - ------ 2 1 + x
(-1.0 + x^2)/(1.0 + x^2)
(1 + x)*(-1 + x) ---------------- 2 1 + x
(1 + x)*(-1 + x)/(1 + x^2)