/ 2\ \1 + x /*atan(x)
(1 + x^2)*atan(x)
1 + 2*x*atan(x)
/ x \ 2*|------ + atan(x)| | 2 | \1 + x /
/ 2 \ | 2*x | 2*|2 - ------| | 2| \ 1 + x / -------------- 2 1 + x