atan(2*x) --------- x
atan(2*x) 2 - --------- + ------------ 2 / 2\ x x*\1 + 4*x /
/ 8 atan(2*x) 2 \ 2*|- ----------- + --------- - -------------| | 2 3 2 / 2\| | / 2\ x x *\1 + 4*x /| \ \1 + 4*x / /
/ 3*atan(2*x) 6 16 128*x \ 2*|- ----------- + ------------- + ------------- + -----------| | 4 3 / 2\ 2 3| | x x *\1 + 4*x / / 2\ / 2\ | \ x*\1 + 4*x / \1 + 4*x / /