Quadratic formula: python treating floats as strings

Question

I am making a program that asks the user to input values for a, b and c which are then used to compute the roots using the quadratic formula. The only problem I have is that python treats a and the square root term as two strings and they are not actually added. The + between them is printed out.

Here is my code:

import cmath

def cubic_formula(a, b, c):
    print("x1: " + str((-b-cmath.sqrt(b**2-4*a*c))/(2*a)))
    print("x2: " + str((-b+cmath.sqrt(b ** 2 - 4 * a * c)) / (2 * a)))

a = float(input("a: ")) b = float(input("b: ")) c = float(input("c: "))

cubic_formula(a, b, c)

And here is the output, illustrating the problem I just described:

I don't know how to make it so that the plus-sign results in an actual addition of the two numbers. Removing the str() and having no strings inside print() did not change anything.

Answer 1

You are witnessing complex numbers, not strings. When the discriminant b*b-4*a*c is negative, the solution is not real valued. The imaginary unit is denoted j in Python and complexes print like (a+bj) in Python. You may want to check if the discriminant is positive before computing, and use the math.sqrt function, which returns a float, instead of the cmath.sqrt function, which returns a complex.

Also note you called the function cubic_formula, but are calculating quadratic_formula.