pi pi*x ------ - ----------- x 2 10 + - / x\ 2 2*|10 + -| \ 2/
pi/(10 + x/2) - pi*x/(2*(10 + x/2)^2)
3.14159265358979/(10.0 + 0.5*x) - 0.015707963267949*x/(1 + 0.05*x)^2
3.14159265358979/(10.0 + 0.5*x) - 0.015707963267949*x/(1 + 0.05*x)^2
2 4*pi*(20 + x) - 4*pi*x*(20 + x) -------------------------------- 3 2*(20 + x)
(4*pi*(20 + x)^2 - 4*pi*x*(20 + x))/(2*(20 + x)^3)