Why do I get math domain error?

Question

Why do I get this error?

I\'m trying to solve an equation like this:

ax^2 + bx + c

Traceback (most recent call last):
  File \"I:/Taller de Progr         


        

Answer 1

The math module (which I suppose you are using) doesn't support complex numbers. Either use cmath (python2 and python3) or the power operator ** (python3).

This should always work, no matter the sign of the discriminant:

x1 = (-b + (b ** 2 - 4 * a * c) ** .5) / 2 / a

Example:

>>> b = 1
>>> a = 2
>>> c = 3
>>> (-b + (b ** 2 - 4 * a * c) ** .5) / 2 / a
(-0.24999999999999992+1.1989578808281798j)

While using math.sqrt with the same values raises the described error:

>>> (-b + sqrt(b ** 2 - a * c)) / (2 * a)
Traceback (most recent call last):
  File "", line 1, in 
ValueError: math domain error