/a + 6*x\ |-------| \ a / ------------- a*x + 6*x*x -----------*a a
a + 6*x -------------- / 2 \ a*\6*x + a*x/
(a + 6.0*x)/(a*(6.0*x^2 + a*x))
1 --- a*x
a + 6*x --------------- a*(a*x + 6*x*x)