import math

def quadratic_equation(a, b, c):

    if (b*b-4*a*c) >= 0:

        x1=(math.sprt(b*b-4*a*c)-b)/(2*a)

        x2=(-(math.sprt(b*b-4*a*c)-b)/(2*a)

        return x1,x2

    else: 

        return None

print quadratic_equation(2, 3, 0)

print quadratic_equation(1, -6, 5)