Considering the equation
a*x^3 + a*x^2 + x + b == 0
I'm looking to find the best value for
x from the above polynomial (with
b known) for which the second function using the same
(65 + 103*a*x^2)/(1 + a*x^2)
gives me the closest
NonlinearModelFit for an already determined set of (x,y) coordinates.