n n-1 1
f(x) = Cn * x + Cn-1 * x + ... + C1 * x + C0
The idea is to make a guess of what the root is and testing if
f(guess) = 0. If not, we improve the guess, and try again.
The formula for improving the guess is:
f(guess)
new guess = guess - ----------
f'(guess)