Implement function which will return sum of roots of a quadratic equation rounded to 2 decimal places, if there are any possible roots, else return **None/null/nil/nothing**. If you use discriminant,when discriminant = 0, x1 = x2 = root => return sum of both roots. There will always be valid arguments. 
Quadratic equation - https://en.wikipedia.org/wiki/Quadratic_equation
def roots(a,b,c):
    import math
    d = b ** 2 - 4 * a * c
    if d > 0:
        return round(-2 * b / (2 * a), 2)
    elif d == 0:
        x = -b / (2 * a)
        return x * 2
    else:
        return None
def roots(a,b,c):
    import math
    d = b ** 2 - 4 * a * c
    if d > 0:
        return round(-2 * b / (2 * a), 2)
    elif d == 0:
        x = -b / (2 * a)
        return x * 2
    else:
        return None