How to write a simple quadratic equation program in Python?

Question

Python

I recently started learning python from Lutz's book and the codecademy course (my first experience in programming). I tried to write a simple program for calculating quadratic equations:

a = input('Введите а:')
b = input('Введите b:')
c = input('Введите c:')
if len(a) > 0 and len(b) > 0 and len(c) > 0 and not a.isalpha() and not b.isalpha() and not c.isalpha():
    d = int(b) ** 2 - 4 * int(a) * int(c)
    if d > 0 or d == 0:
        import math
        dd = math.sqrt(d)
        x = - int(b) - int(dd) / (int(a) * 2)
        x1 = - int(b) + int(dd) / (int(a) * 2)
        print (x, x1)
    else:
        print ('Рещений не имеет')
else:
    print ('Введите только числа')

Actually, the x's are calculated incorrectly, before that everything is done correctly.
Please explain what is my mistake?

Answer 1

x = ( -int(b) - int(dd) ) / (int(a) * 2)
x1 = ( -int(b) + int(dd) ) / (int(a) * 2)

Answer 2

Reading a quadratic equation in integers is so unusual.

Answer 3

If d = 0, then it is desirable to display one root, don't you think?