Implement a better zero-finding algorithm

[abelsiqueira]

Currently, we use the bisection method to compute the zero of the function f. Instead, we could implement regula falsi, which is very similar and easy to swap.
A full description is https://en.wikipedia.org/wiki/Regula_falsi but the only part that matters is that instead of

x = (a + b) / 2

we use

x = (a * fb - b * fa) / (fb - fa)